Custom domain not working

[mocodev]

Custom domain does not appear to be working when pressing the "checkout" button in the cart drawer.

var client = ShopifyBuy.buildClient({
					domain: 'XXXX',
					storefrontAccessToken: 'XXX',
				});

This was working as we have made no changes to our code/implementation. We know that storefrontAccessToken is working as we're able to add/remove things from the cart. But whatever value we add for domain: it does not honor.

Did something change?