Epic: ECE and Subscription products

[bborman22]

This epic is to help us track our progress and compatibility with the mix of combinations available to subscription products covering: variable subscriptions, virtual products, free trials, and sign up fees. @asumaran had done some great work and generated the following chart to show our availability currently and we've been using that to map out our next steps. I'm finally creating this issue to keep any remainder of that discussion and planning in one place going forward.

Case	is Variable subscription	is virtual	Free Trial	Sign Up Fee	Expected	Actual	Observations
1	No	no	No	No	✅	✅
2	No	no	No	Yes	✅	✅
3	No	no	Yes	No	❌	❌	currently we don’t support subscriptions that need shipping with free trials. ref Captured by #8152
4	No	no	Yes	Yes	❌ (we should though)	❌	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799). Captured by #9776
5	no	yes	No	No	✅	✅
6	no	yes	No	Yes	✅	✅
7	no	yes	Yes	No	✅	✅	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799). Uses Stripe Setup Intents API, charges $0, this is great.
8	no	yes	Yes	Yes	✅	✅	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799) . ✅ Cart and Checkout pages show correct and amount and charges accordingly.
9	yes	no	no	No	✅	✅	Product Page: ECE appears on page load while no variation is selected. Alerts to choose a variation on click.
10	yes	no	no	Yes	✅	✅
11	yes	no	Yes	No	❌ (should we?)	❌	Currently, not supported. Captured by #8152
12	yes	no	Yes	Yes	❌ (we should)	❌	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799). Captured by #9776
13	yes	Yes	No	No	✅	✅
14	yes	Yes	No	Yes	✅	✅
15	yes	Yes	Yes	No	✅	✅	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799). Fixed by #9897 and #9917
16	yes	Yes	Yes	Yes	✅	✅	❌ Product Page: amount in payment sheet is incorrect. Although the final charged amount is correct (captured by #9799). Fixed by #9897 and #9917

ECE Subscription Compatibility

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1. ECE buttons not rendered for variable subscription products on the product details page #9771
   focus: checkout payments priority: high type: bug +3
   
2. ECE does not render on PDP when subscription product has a free trial but has a non-zero signup fee #9776
   focus: checkout payments priority: medium type: bug +3
   
3. Getting PRBs to show up on the cart/checkout page for any subscription that has a free trial. #8152
   category: core component: wcpay subscriptions focus: checkout payments priority: high type: bug +5
4. ECE - Misleading line item payment details for subscriptions with signup fee and a free triel #9799
   focus: checkout payments priority: medium status: on hold type: bug +4

[asumaran]

Tokenized Carts for ECE allows us to retrieve the exact amounts the user will be charged, resolving many issues but also introducing new challenges. Since this new implementation for ECE is about to be introduced, we will pause work on the ECE fixes for subscriptions to avoid making changes based on the soon-to-be deprecated implementation. We will wait for Tokenized ECE to be enabled by default.

I’ve tested all the cases related to this issue using #10099 with Tokenized Carts enabled. Which is the latest work related to this issue. And I can confirm that almost everything that was already working continues to work correctly with tokenized ECE, but I’ve noticed some new bugs:

For example, in cases 7, 12, and 15, ECE doesn’t work because the total amount to be paid is zero, and ECE doesn’t accept zero as a valid total. The payable amount is correct, but it can’t be used for ECE. I’m not sure how to proceed here.

In cases 4 and 12, we have another issue (Originally reported here paJDYF-g3R-p2#comment-27550) The selected shipping option is not applied to the initial order, and the renewal order receives the first available shipping option, even though it was never selected. This is a bug.

In case 12 we also have another bug which is the same as @cesarcosta99 discovered here. ECE fails to open after closing the payment sheet. I plan to fix this as part of #10099

cc @bborman22 @pierorocca