“DID_FAIL_TO_RENEW”

I'll preface by saying I'm very new to working with Apple subscriptions and my question is probably quite silly, but I can't find any information on this topic. What I am currently stumped about is the handling of grace periods for service-level downgrades that have experienced billing failure. As an example, the user wants to downgrade from Product B to Product A. The products are in different service levels and have different durations, so the downgrade is scheduled for the next renewal. When that time comes, billing fails and our server receives a DID_FAIL_TO_RENEW notification. How should such a case be handled? If a grace period is in place, should that grace period apply to the original subscription (to Product B), the new subscription (to Product A) or both? Thanks in advance

When does Apple plan to support a server notification for when a subscription auto renews? Best I can tell from the documentation and online articles there doesn't appear to be a notification type for this scenario. There are notifications when a renewal fails because of billing issues (ie DID_FAIL_TO_RENEW), when a previously expired subscription gets renewed (ie DID_RECOVER), and when a user interactively triggers a renewal (ie INTERACTIVE_RENEWAL). But nothing for when a user transitions from say a trial to an automatic renewal. Seems like a pretty big gap for a subscription-based notification system.

I tried multi sandbox account and read this post: https://forums.developer.apple.com/thread/130456We have the same problem for some accounts: DID_FAIL_TO_RENEW and the expiration_intent = 4 (The product was not available for purchase at the time of renewal.)While if we tried a new account or simply buy the goods manually, it works and gives us a new transaction id.Because of the experience, I can't test the auto subscription. I read the document and it said the transaction id is unique for buying and renewal, but I never see new transaction-id except manually buy.Is it a regular performance?

Our Server always receive about DID_FAIL_TO_RENEW when first subscription