diff --git a/README.md b/README.md
index afc7d57..4b8f1ef 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,9 @@ If you are an AI agent implementing this SDK, follow the steps below exactly. If
 
 If they are on the receive side, ask one follow-up:
 - **Platform** — single-tenant, one API key.
-- **Parent Platform** — multi-tenant, manages multiple child platforms each with their own API key and HMAC secret.
+- **Parent Platform** — multi-tenant, manages multiple child platforms. Two variants:
+  - **Per-client keys** — each child has its own API key and HMAC secret; you scope requests per-call.
+  - **Shared key** — one API key and HMAC secret for all children; tag the child per-payment with `setChildPlatform()`.
 
 **2. Follow the matching Quick Start section below.**
 
@@ -47,9 +49,13 @@ Receive side (platforms):
 - Always call `.setZk()` on the `PaymentBuilder` before calling `addPaymentAsync`. Plain-text destinations are rejected in `strict` mode.
 - Store the `secret` from `AddPaymentResult` alongside the invoice — it is required to reconstruct the verify URL for the wallet.
 
-Receive side (parent platforms), in addition to the platform rules:
-- Include `hmacSecret` in `BrantaClientOptions`.
-- Pass per-call `BrantaClientOptions` to scope requests to the correct child platform's API key.
+Receive side (parent platforms — per-client keys), in addition to the platform rules:
+- Include `hmacSecret` in `BrantaClientOptions` but omit `defaultApiKey` at service setup.
+- Pass per-call `BrantaClientOptions` with each child's API key to scope requests.
+
+Receive side (parent platforms — shared key), in addition to the platform rules:
+- Include both `defaultApiKey` and `hmacSecret` in `BrantaClientOptions`.
+- Call `.setChildPlatform(name, logoUrl: ..., logoLightUrl: ...)` on the builder to tag each payment with the child's branding.
 
 # Quick Start
 
@@ -155,7 +161,12 @@ final result = await service.addPaymentAsync(payment);
 
 ## For Parent Platforms (Receive Side)
 
-Parent platforms sign requests with HMAC in addition to the API key. Pass per-call `BrantaClientOptions` to scope requests to each child platform.
+Parent platforms sign requests with HMAC. Choose a variant based on how API keys are structured.
+
+<details>
+<summary>Shared key — one API key covers all children (Recommended)</summary>
+
+Set up with a single API key and HMAC secret; identify the child platform per-payment.
 
 ```dart
 import 'package:branta/branta.dart';
@@ -163,7 +174,7 @@ import 'package:http/http.dart' as http;
 
 final options = BrantaClientOptions(
   baseUrl: BrantaServerBaseUrl.staging,
-  defaultApiKey: '<api-key>',
+  defaultApiKey: '<shared-api-key>',
   hmacSecret: '<hmac-secret>',
   privacy: PrivacyMode.strict,
 );
@@ -178,12 +189,52 @@ final payment = PaymentBuilder()
     .setDescription('Order #1234')
     .addDestination('1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa')
     .setZk()
+    .setChildPlatform('ChildBrand', logoUrl: 'https://example.com/logo.png')
     .setTtl(600)
     .build();
 
 final result = await service.addPaymentAsync(payment);
 ```
 
+</details>
+
+<details>
+<summary>Per-client keys — each child has its own API key</summary>
+
+Set up the service with the shared HMAC secret only; pass each child's API key per-call.
+
+```dart
+import 'package:branta/branta.dart';
+import 'package:http/http.dart' as http;
+
+final options = BrantaClientOptions(
+  baseUrl: BrantaServerBaseUrl.staging,
+  hmacSecret: '<hmac-secret>',
+  privacy: PrivacyMode.strict,
+);
+final brantaClient = BrantaClient(httpClient: http.Client(), defaultOptions: options);
+final service = BrantaService(
+  client: brantaClient,
+  aesEncryption: AesEncryptionService(),
+  defaultOptions: options,
+);
+
+final payment = PaymentBuilder()
+    .setDescription('Order #1234')
+    .addDestination('1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa')
+    .setZk()
+    .setTtl(600)
+    .build();
+
+// Scope to the child platform's API key per-call
+final result = await service.addPaymentAsync(
+  payment,
+  options: BrantaClientOptions(defaultApiKey: '<child-api-key>'),
+);
+```
+
+</details>
+
 # Privacy
 
 `PrivacyMode` controls whether plain-text on-chain lookups are allowed.
diff --git a/lib/src/v2/classes/payment_builder.dart b/lib/src/v2/classes/payment_builder.dart
index 45260e7..08b11fc 100644
--- a/lib/src/v2/classes/payment_builder.dart
+++ b/lib/src/v2/classes/payment_builder.dart
@@ -3,6 +3,7 @@ import 'package:uuid/uuid.dart';
 import '../../enums/destination_type.dart';
 import '../models/destination.dart';
 import '../models/payment.dart';
+import '../models/platform.dart';
 
 class PaymentBuilder {
   final Payment _payment = Payment(destinations: []);
@@ -50,5 +51,10 @@ class PaymentBuilder {
     return this;
   }
 
+  PaymentBuilder setChildPlatform(String name, {String? logoUrl, String? logoLightUrl}) {
+    _payment.childPlatform = Platform(name: name, logoUrl: logoUrl, logoLightUrl: logoLightUrl);
+    return this;
+  }
+
   Payment build() => _payment;
 }
diff --git a/lib/src/v2/models/payment.dart b/lib/src/v2/models/payment.dart
index fdb2d94..0fbc1b3 100644
--- a/lib/src/v2/models/payment.dart
+++ b/lib/src/v2/models/payment.dart
@@ -11,6 +11,7 @@ class Payment {
   String? platformLogoUrl;
   String? platformLogoLightUrl;
   Platform? parentPlatform;
+  Platform? childPlatform;
   String? btcPayServerPluginVersion;
 
   /// Runtime-only flag set by [BrantaService] after metadata decryption.
@@ -27,6 +28,7 @@ class Payment {
     this.platformLogoUrl,
     this.platformLogoLightUrl,
     this.parentPlatform,
+    this.childPlatform,
     this.btcPayServerPluginVersion,
   });
 
@@ -67,6 +69,7 @@ class Payment {
         if (platformLogoLightUrl != null)
           'platform_logo_light_url': platformLogoLightUrl,
         if (parentPlatform != null) 'parent_platform': parentPlatform!.toJson(),
+        if (childPlatform != null) 'child_platform': childPlatform!.toJson(),
         if (btcPayServerPluginVersion != null)
           'btc_pay_server_plugin_version': btcPayServerPluginVersion,
       };
diff --git a/test/branta_test.dart b/test/branta_test.dart
index d75a699..e2d786f 100644
--- a/test/branta_test.dart
+++ b/test/branta_test.dart
@@ -670,6 +670,68 @@ void main() {
       final dest = Destination(value: 'addr');
       expect(dest.toJson().containsKey('type'), isFalse);
     });
+
+    test('setChildPlatform sets name', () {
+      final payment = PaymentBuilder()
+          .addDestination(_bitcoinAddress)
+          .setChildPlatform('Acme')
+          .build();
+
+      expect(payment.childPlatform!.name, equals('Acme'));
+    });
+
+    test('setChildPlatform optional URLs default to null', () {
+      final payment = PaymentBuilder()
+          .addDestination(_bitcoinAddress)
+          .setChildPlatform('Acme')
+          .build();
+
+      expect(payment.childPlatform!.logoUrl, isNull);
+      expect(payment.childPlatform!.logoLightUrl, isNull);
+    });
+
+    test('setChildPlatform with URLs sets urls', () {
+      final payment = PaymentBuilder()
+          .addDestination(_bitcoinAddress)
+          .setChildPlatform('Acme',
+              logoUrl: 'https://example.com/logo.png',
+              logoLightUrl: 'https://example.com/logo-light.png')
+          .build();
+
+      expect(payment.childPlatform!.logoUrl, equals('https://example.com/logo.png'));
+      expect(payment.childPlatform!.logoLightUrl, equals('https://example.com/logo-light.png'));
+    });
+
+    test('setChildPlatform returns builder', () {
+      final builder = PaymentBuilder().addDestination(_bitcoinAddress);
+      final result = builder.setChildPlatform('Acme');
+
+      expect(result, same(builder));
+    });
+
+    test('setChildPlatform serializes to toJson', () {
+      final payment = PaymentBuilder()
+          .addDestination(_bitcoinAddress)
+          .setChildPlatform('Acme', logoUrl: 'https://example.com/logo.png')
+          .build();
+
+      final json = payment.toJson();
+      final cp = json['child_platform'] as Map<String, dynamic>;
+
+      expect(cp['name'], equals('Acme'));
+      expect(cp['logo_url'], equals('https://example.com/logo.png'));
+      expect(cp.containsKey('logo_light_url'), isFalse);
+    });
+
+    test('no childPlatform omitted from toJson', () {
+      final payment = PaymentBuilder()
+          .addDestination(_bitcoinAddress)
+          .build();
+
+      final json = payment.toJson();
+
+      expect(json.containsKey('child_platform'), isFalse);
+    });
   });
 
   // -------------------------------------------------------------------------