Promised Payment (Grace Period)
You can activate Promised Payment (grace period) under Other → Profile&Settings → Promised Payment, in case it’s not possible for you to extend your subscription at the moment.
You can use a grace period for 5 days after the expiration of your subscription. The grace period lasts for 5 days from the moment it is granted.
The days under the grace period will be deducted from the length of the subscription once it is paid for.
If you pay for your subscription through Apple, in-app credit is not available.