There should be minimal delay between you enabling grace periods for your app and it applying to customers who newly experience billing failures. If you haven't already, check out these articles to ensure you understand grace period and how to enable it for your app:
https://developer.apple.com/documentation/storekit/in-app_purchase/original_api_for_in-app_purchase/subscriptions_and_offers/reducing_involuntary_subscriber_churn
https://help.apple.com/app-store-connect/#/dev58bda3212
If you've enabled grace periods and you see receipts with is_in_billing_retry_period="1"
but no grace_period_expires_date
field, that could indicate an issue, as you should see both. If that's the case, please file a Feedback Ticket and post the FB number here so we can help investigate. Include as much information in the ticket as you can, such as the app identifier, subscription product, and most importantly the erroneous receipt with the missing grace_period_expires_date
.
http://feedbackassistant.apple.com