diff --git a/simple_subscription/locale/de.po b/simple_subscription/locale/de.po
index 5872677..6a7ca67 100644
--- a/simple_subscription/locale/de.po
+++ b/simple_subscription/locale/de.po
@@ -28,6 +28,12 @@ msgstr ""
 msgid "Accounts User"
 msgstr ""
 
+#. Label of the additional_customer_data_section (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Additional Customer Data"
+msgstr "Zusätzliche Kundendaten"
+
 #. Label of the amended_from (Link) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Amended From"
@@ -38,6 +44,23 @@ msgstr ""
 msgid "Biennial"
 msgstr "Zweijährlich"
 
+#. Label of the billing_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address"
+msgstr ""
+
+#. Label of the customer_address (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address Name"
+msgstr ""
+
+#. Label of the contact_person (Link) field in DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Contact Name"
+msgstr "Name des Rechnungskontakts"
+
 #. Label of the period_type (Select) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Billing Period is based on"
@@ -53,7 +76,13 @@ msgstr "Rechnungszeit"
 msgid "Company"
 msgstr "Unternehmen"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:28
+#. Label of the contact_display (Small Text) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Contact"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:73
 msgid "Create current {0} invoice"
 msgstr "Aktuelle {0} Rechnung erstellen"
 
@@ -89,7 +118,7 @@ msgstr ""
 msgid "Disabled"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:135
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:195
 msgid "Failed to create subscription invoice"
 msgstr "Fehler beim Erstellen der Abo-Rechnung"
 
@@ -129,15 +158,21 @@ msgstr ""
 msgid "Monthly"
 msgstr "Monatlich"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:57
+#. Description of the 'Additional Customer Data' (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Optional. If empty, defaults are set on invoice generation"
+msgstr "Optional. Wenn leer, werden bei der Rechnungserstellung die Standardwerte gesetzt."
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:107
 msgid "Please amend Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte ändern Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:51
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:101
 msgid "Please enable Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte aktivieren Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:54
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:104
 msgid "Please submit Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte buchen Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
@@ -151,7 +186,7 @@ msgstr ""
 msgid "Quarterly"
 msgstr "Vierteljährlich"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:124
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:184
 msgid "Sales Invoice already exists for this period: {}"
 msgstr "Rechnung für diese Periode existiert bereits: {}"
 
@@ -160,6 +195,18 @@ msgstr "Rechnung für diese Periode existiert bereits: {}"
 msgid "Selling"
 msgstr ""
 
+#. Label of the shipping_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address"
+msgstr ""
+
+#. Label of the shipping_address_name (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address Name"
+msgstr ""
+
 #. Name of a DocType
 #. Label of a Link in the Simple Subscription Selling Workspace
 #. Label of a shortcut in the Simple Subscription Selling Workspace
@@ -184,8 +231,7 @@ msgstr "Vertrieb"
 msgid "Start Date"
 msgstr "Startdatum"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:209
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:221
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:271
 msgid "Start Date is required for frequency {0}."
 msgstr "Startdatum ist für die Frequenz {0} erforderlich."
 
@@ -233,3 +279,6 @@ msgstr "Kalendermonate"
 msgid "start date"
 msgstr "Startdatum"
 
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:90
+msgid "{0} {1} does not belong to Customer {2}."
+msgstr "{0} {1} gehört nicht zu Kunde {2}."
diff --git a/simple_subscription/locale/main.pot b/simple_subscription/locale/main.pot
index a8c2ac1..3d6e406 100644
--- a/simple_subscription/locale/main.pot
+++ b/simple_subscription/locale/main.pot
@@ -26,6 +26,12 @@ msgstr ""
 msgid "Accounts User"
 msgstr ""
 
+#. Label of the additional_customer_data_section (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Additional Customer Data"
+msgstr ""
+
 #. Label of the amended_from (Link) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Amended From"
@@ -36,6 +42,23 @@ msgstr ""
 msgid "Biennial"
 msgstr ""
 
+#. Label of the billing_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address"
+msgstr ""
+
+#. Label of the customer_address (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address Name"
+msgstr ""
+
+#. Label of the contact_person (Link) field in DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Contact Name"
+msgstr ""
+
 #. Label of the period_type (Select) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Billing Period is based on"
@@ -51,7 +74,13 @@ msgstr ""
 msgid "Company"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:28
+#. Label of the contact_display (Small Text) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Contact"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:73
 msgid "Create current {0} invoice"
 msgstr ""
 
@@ -87,7 +116,7 @@ msgstr ""
 msgid "Disabled"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:135
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:195
 msgid "Failed to create subscription invoice"
 msgstr ""
 
@@ -127,15 +156,21 @@ msgstr ""
 msgid "Monthly"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:57
+#. Description of the 'Additional Customer Data' (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Optional. If empty, defaults are set on invoice generation"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:107
 msgid "Please amend Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:51
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:101
 msgid "Please enable Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:54
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:104
 msgid "Please submit Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
@@ -149,7 +184,7 @@ msgstr ""
 msgid "Quarterly"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:124
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:184
 msgid "Sales Invoice already exists for this period: {}"
 msgstr ""
 
@@ -158,6 +193,18 @@ msgstr ""
 msgid "Selling"
 msgstr ""
 
+#. Label of the shipping_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address"
+msgstr ""
+
+#. Label of the shipping_address_name (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address Name"
+msgstr ""
+
 #. Name of a DocType
 #. Label of a Link in the Simple Subscription Selling Workspace
 #. Label of a shortcut in the Simple Subscription Selling Workspace
@@ -182,8 +229,7 @@ msgstr ""
 msgid "Start Date"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:209
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:221
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:271
 msgid "Start Date is required for frequency {0}."
 msgstr ""
 
@@ -231,3 +277,6 @@ msgstr ""
 msgid "start date"
 msgstr ""
 
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:90
+msgid "{0} {1} does not belong to Customer {2}."
+msgstr ""
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
index 9f89807..e7603db 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
@@ -1,8 +1,25 @@
 // Copyright (c) 2022, ALYF GmbH and contributors
 // For license information, please see license.txt
 
+function customer_link_query(frm, query) {
+	return {
+		query: query,
+		filters: { link_doctype: "Customer", link_name: frm.doc.customer },
+	};
+}
+
 frappe.ui.form.on("Simple Subscription", {
 	setup: function (frm) {
+		for (const field of ["customer_address", "shipping_address_name"]) {
+			frm.set_query(field, () =>
+				customer_link_query(frm, "frappe.contacts.doctype.address.address.address_query")
+			);
+		}
+
+		frm.set_query("contact_person", () =>
+			customer_link_query(frm, "frappe.contacts.doctype.contact.contact.contact_query")
+		);
+
 		frm.set_query("item", "items", function () {
 			return {
 				filters: {
@@ -21,6 +38,39 @@ frappe.ui.form.on("Simple Subscription", {
 		});
 	},
 
+	customer: function (frm) {
+		// address and contact are customer specific, don't keep the previous customer's
+		for (const field of ["customer_address", "shipping_address_name", "contact_person"]) {
+			frm.set_value(field, null);
+		}
+	},
+
+	customer_address: function (frm) {
+		erpnext.utils.get_address_display(frm, "customer_address", "billing_address_display");
+	},
+
+	shipping_address_name: function (frm) {
+		erpnext.utils.get_address_display(frm, "shipping_address_name", "shipping_address_display");
+	},
+
+	contact_person: function (frm) {
+		const contact = frm.doc.contact_person;
+		if (!contact) {
+			frm.set_value("contact_display", "");
+			return;
+		}
+
+		frappe.call({
+			method: "frappe.contacts.doctype.contact.contact.get_contact_details",
+			args: { contact },
+			callback: (r) =>
+				// the selection may have moved on while the call was in flight
+				r.message &&
+				frm.doc.contact_person === contact &&
+				frm.set_value("contact_display", r.message.contact_display),
+		});
+	},
+
 	refresh: function (frm) {
 		if (frm.doc.docstatus !== 1 || frm.doc.disabled === 1) return;
 
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
index 4c0d406..c089041 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
@@ -17,6 +17,14 @@
   "billing_time",
   "frequency",
   "disabled",
+  "additional_customer_data_section",
+  "customer_address",
+  "billing_address_display",
+  "shipping_address_name",
+  "shipping_address_display",
+  "column_break_beul",
+  "contact_person",
+  "contact_display",
   "section_break_5",
   "items",
   "section_break_7",
@@ -125,6 +133,59 @@
    "label": "Currency",
    "options": "Currency",
    "reqd": 1
+  },
+  {
+   "collapsible": 1,
+   "description": "Optional. If empty, defaults are set on invoice generation",
+   "fieldname": "additional_customer_data_section",
+   "fieldtype": "Section Break",
+   "label": "Additional Customer Data"
+  },
+  {
+   "allow_on_submit": 1,
+   "fieldname": "customer_address",
+   "fieldtype": "Link",
+   "label": "Billing Address Name",
+   "options": "Address"
+  },
+  {
+   "fieldname": "billing_address_display",
+   "fieldtype": "Text Editor",
+   "is_virtual": 1,
+   "label": "Billing Address",
+   "read_only": 1
+  },
+  {
+   "allow_on_submit": 1,
+   "fieldname": "shipping_address_name",
+   "fieldtype": "Link",
+   "label": "Shipping Address Name",
+   "options": "Address"
+  },
+  {
+   "fieldname": "shipping_address_display",
+   "fieldtype": "Text Editor",
+   "is_virtual": 1,
+   "label": "Shipping Address",
+   "read_only": 1
+  },
+  {
+   "fieldname": "column_break_beul",
+   "fieldtype": "Column Break"
+  },
+  {
+   "allow_on_submit": 1,
+   "fieldname": "contact_person",
+   "fieldtype": "Link",
+   "label": "Billing Contact Name",
+   "options": "Contact"
+  },
+  {
+   "fieldname": "contact_display",
+   "fieldtype": "Small Text",
+   "is_virtual": 1,
+   "label": "Contact",
+   "read_only": 1
   }
  ],
  "is_submittable": 1,
@@ -134,7 +195,7 @@
    "link_fieldname": "simple_subscription"
   }
  ],
- "modified": "2026-06-15 11:53:49.870013",
+ "modified": "2026-09-07 14:24:50.615780",
  "modified_by": "Administrator",
  "module": "Simple Subscription",
  "name": "Simple Subscription",
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
index 8571c7f..8682130 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
@@ -8,6 +8,8 @@
 from erpnext.accounts.doctype.sales_invoice.sales_invoice import SalesInvoice
 from erpnext.accounts.party import get_party_details
 from frappe import _
+from frappe.contacts.doctype.address.address import get_address_display
+from frappe.contacts.doctype.contact.contact import get_contact_details
 from frappe.model.document import Document
 from frappe.utils import today
 
@@ -41,9 +43,59 @@ class BillingTime(Enum):
 	AfterEndOfPeriod = "after end of period"
 
 
+# forwarded to the Sales Invoice, which uses the same fieldnames
+CUSTOMER_LINK_FIELDS: dict[str, str] = {
+	"customer_address": "Address",
+	"shipping_address_name": "Address",
+	"contact_person": "Contact",
+}
+
+
 class SimpleSubscription(Document):
+	@property
+	def billing_address_display(self) -> str | None:
+		return get_address_display(self.customer_address)
+
+	@property
+	def shipping_address_display(self) -> str | None:
+		return get_address_display(self.shipping_address_name)
+
+	@property
+	def contact_display(self) -> str | None:
+		if not self.contact_person:
+			return None
+		return frappe.db.get_value("Contact", self.contact_person, "full_name")
+
 	def validate(self):
 		validate_calendar_frequencies(self.period_type, self.frequency, self.start_date)
+		self.validate_customer_links()
+
+	def before_update_after_submit(self):
+		self.validate_customer_links()
+
+	def validate_customer_links(self) -> None:
+		"""The .js queries filter by customer, but the customer can change afterwards."""
+		for fieldname, doctype in CUSTOMER_LINK_FIELDS.items():
+			name = self.get(fieldname)
+			if not name:
+				continue
+
+			if not frappe.db.exists(
+				"Dynamic Link",
+				{
+					"parenttype": doctype,
+					"parent": name,
+					"link_doctype": "Customer",
+					"link_name": self.customer,
+				},
+			):
+				frappe.throw(
+					_("{0} {1} does not belong to Customer {2}.").format(
+						_(self.meta.get_label(fieldname)),
+						frappe.bold(name),
+						frappe.bold(self.customer),
+					)
+				)
 
 	def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		msg = None
@@ -62,6 +114,8 @@ def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		invoice = frappe.new_doc("Sales Invoice")
 		invoice.company = self.company
 		invoice.customer = self.customer
+		invoice.customer_address = self.customer_address
+		invoice.shipping_address_name = self.shipping_address_name
 		invoice.selling_price_list = self.get_price_list()
 		for row in self.items:
 			invoice.append(
@@ -76,6 +130,9 @@ def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		invoice.to_date = to_date
 		invoice.simple_subscription = self.name
 		invoice.set_missing_values()
+		if self.contact_person:
+			# set_missing_values() would have filled in the customer's primary contact instead
+			invoice.update(get_contact_details(self.contact_person))
 		return invoice.insert()
 
 	def get_price_list(self) -> str | None:
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
index efa1d60..e9569ee 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
@@ -7,6 +7,7 @@
 import frappe
 
 from .simple_subscription import (
+	CUSTOMER_LINK_FIELDS,
 	BillingTime,
 	Frequency,
 	PeriodType,
@@ -196,3 +197,140 @@ def test_get_from_and_to_date(self):
 		)
 		self.assertEqual(from_date, date(2020, 1, 1))
 		self.assertEqual(to_date, date(2021, 12, 31))
+
+
+class TestSubscriptionCustomerData(unittest.TestCase):
+	"""Customer-bound Address/Contact links: the ownership check and the display properties.
+
+	Kept deliberately light. Generating the invoice needs a fully set-up ERPNext site -- Company,
+	Item Group, UOM, Price List, Fiscal Year -- fixtures that only the setup wizard creates and
+	that CI (a bare `install-app erpnext`) does not have. So these exercise the app's own logic on
+	an in-memory document, plus a meta check that the fieldnames create_invoice() forwards still
+	line up with the Sales Invoice.
+	"""
+
+	@classmethod
+	def setUpClass(cls):
+		super().setUpClass()
+		# never committed, so the fixtures die with the transaction -- same as IntegrationTestCase
+		cls.addClassCleanup(frappe.db.rollback)
+		make_default_address_template()
+		cls.customer = make_customer("_Test Sub Customer")
+		cls.other_customer = make_customer("_Test Sub Other Customer")
+		cls.address = make_address("_Test Sub Billing", cls.customer, "Rechnungsweg 1")
+		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer, "Fremdweg 3")
+		cls.contact = make_contact("_Test Sub Contact", cls.customer)
+		cls.other_contact = make_contact("_Test Sub Foreign Contact", cls.other_customer)
+
+	def make_subscription(self, **kwargs):
+		subscription = frappe.new_doc("Simple Subscription")
+		subscription.customer = self.customer
+		subscription.update(kwargs)
+		return subscription
+
+	def test_accepts_links_of_the_same_customer(self):
+		subscription = self.make_subscription(
+			customer_address=self.address,
+			shipping_address_name=self.address,
+			contact_person=self.contact,
+		)
+		subscription.validate_customer_links()  # must not raise
+
+	def test_accepts_empty_links(self):
+		self.make_subscription().validate_customer_links()  # must not raise
+
+	def test_rejects_links_of_another_customer(self):
+		for fieldname, value in (
+			("customer_address", self.other_address),
+			("shipping_address_name", self.other_address),
+			("contact_person", self.other_contact),
+		):
+			with self.subTest(fieldname=fieldname):
+				subscription = self.make_subscription(**{fieldname: value})
+				self.assertRaisesRegex(
+					frappe.ValidationError,
+					"does not belong to Customer",
+					subscription.validate_customer_links,
+				)
+
+	def test_guards_the_links_after_submit_too(self):
+		"""The fields are allow_on_submit, so validate() no longer runs once they change."""
+		meta = frappe.get_meta("Simple Subscription")
+		for fieldname in CUSTOMER_LINK_FIELDS:
+			self.assertTrue(meta.get_field(fieldname).allow_on_submit, fieldname)
+
+		subscription = self.make_subscription(customer_address=self.other_address)
+		self.assertRaisesRegex(
+			frappe.ValidationError,
+			"does not belong to Customer",
+			subscription.before_update_after_submit,
+		)
+
+	def test_display_properties_render_linked_records(self):
+		subscription = self.make_subscription(
+			customer_address=self.address,
+			shipping_address_name=self.address,
+			contact_person=self.contact,
+		)
+
+		self.assertIn("Rechnungsweg 1", subscription.billing_address_display)
+		self.assertIn("Rechnungsweg 1", subscription.shipping_address_display)
+		self.assertEqual(subscription.contact_display, "_Test Sub Contact")
+
+	def test_display_properties_are_empty_without_links(self):
+		subscription = self.make_subscription()
+
+		self.assertIsNone(subscription.billing_address_display)
+		self.assertIsNone(subscription.shipping_address_display)
+		self.assertIsNone(subscription.contact_display)
+
+	def test_link_fields_match_the_sales_invoice(self):
+		"""create_invoice() forwards these by name, so both doctypes have to spell them the same.
+
+		The forwarding itself needs a set-up site to exercise, so this is what guards it: a
+		renamed or retyped field on either side breaks the invoice silently, and fails here.
+		"""
+		subscription_meta = frappe.get_meta("Simple Subscription")
+		invoice_meta = frappe.get_meta("Sales Invoice")
+		for fieldname, doctype in CUSTOMER_LINK_FIELDS.items():
+			with self.subTest(fieldname=fieldname):
+				self.assertEqual(subscription_meta.get_field(fieldname).options, doctype)
+				self.assertEqual(invoice_meta.get_field(fieldname).options, doctype)
+
+
+def make_default_address_template() -> None:
+	"""Address.validate() renders the address, which needs one. A bare CI site has none."""
+	if not frappe.db.exists("Address Template", {"is_default": 1}):
+		frappe.get_doc(doctype="Address Template", country="Germany", is_default=1).insert()
+
+
+def make_customer(name: str) -> str:
+	if not frappe.db.exists("Customer", name):
+		frappe.get_doc(doctype="Customer", customer_name=name).insert()
+	return name
+
+
+def make_address(title: str, customer: str, line1: str) -> str:
+	name = f"{title}-Billing"
+	if not frappe.db.exists("Address", name):
+		frappe.get_doc(
+			doctype="Address",
+			address_title=title,
+			address_type="Billing",
+			address_line1=line1,
+			city="Berlin",
+			country="Germany",
+			links=[{"link_doctype": "Customer", "link_name": customer}],
+		).insert()
+	return name
+
+
+def make_contact(first_name: str, customer: str) -> str:
+	name = f"{first_name}-{customer}"
+	if not frappe.db.exists("Contact", name):
+		frappe.get_doc(
+			doctype="Contact",
+			first_name=first_name,
+			links=[{"link_doctype": "Customer", "link_name": customer}],
+		).insert()
+	return name