Amazon Pay ECE: compatibility with Subscriptions

[annemirasol]

Tasks

• Run through Subscription-related critical flows using Amazon Pay.
• Document in-ticket flows that have been tested, e.g. purchasing a subscription using Amazon Pay inside the classic checkout page.
• Address any issues that surface, or create Github issues for them.

[hsingyuc]

We should enable ECE buttons for the synchronized subscription products that include the subscription fee because we charge the subscription fee upfront. Issue #3905

Not related to the Amazon Pay question:
I noticed that the initial order is being created only for the subscription fee, but the order item name uses the product name. Shouldn’t the order item name be "subscription fee" instead of the product name to reduce confusion?

[malithsen]

User Type	Test	Status	Notes
Shopper	Purchase a subscription product	✅
Shopper	Purchase a trial subscription	⚠️	ECE buttons not displayed. See #3623
Shopper	Purchase multiple subscriptions (same schedule)	✅
Shopper	Purchase multiple subscriptions (differing schedules)	✅
Shopper	Renew subscription	✅	We're able to renew the subscription using an existing card but the original payment method used is not saved to the store. See:
Shopper	Change payment method to new card	⚠️	ECE payment methods are not displayed. I guess this is expected.
Shopper	Change payment method to saved card	✅	This doesn't really involve any Amazon Pay specific flows, we're mostly checking if we can change the payment method of a subscription that was initially purchased with Amazon Pay to something else.
Shopper	Change default payment method	✅	Same as above.
Merchant	Renew subscription automatically	❌	Payment method is not saved in the store, resulting in renewal failures. See: #3938
Merchant	Renew subscription manually	⚠️	ECE payment methods are not displayed. I guess this is expected.

[annemirasol]

With #4008, Amazon Pay should now be fully compatible with Subscriptions.