Hey @Tran Hien ,
A billing issue is what we sent wen a payment fails in result of payment issues from the respective store. RevenueCat will only send one billing issue event -- additional payment failures won't trigger additional billing issue events, unless a renewal is successful between payment failures or the subscription ends and is restarted. Once the billing issue is detected, a grace period will start.
When a subscription enters a grace period, RevenueCat detects the change automatically. Users will retain access to their subscriptions, but we'll immediately send events indicating the subscription has been cancelled. These subscriptions are considered cancelled because they are now past due, but will not be considered expired until the end of their grace period. During this time, a subscription may convert to paid through additional billing attempts from the store or by the customer updating their billing information.
For more information on billing issues, we have a useful document here: https://www.revenuecat.com/docs/how-grace-periods-work