Is RevenueCat really using UTC as the time zone?

Hi ​@adib-zaini, this is due to the App Store processing renewals prior to the end of the current subscription period. Commonly, we observe Apple processing the renewal about 8hrs prior to the end of the period. If you’re using Server Notifications, we’re notified as soon as this happens and will dispatch events/webhooks accordingly.

In our RENEWAL events, here is what our timestamps represent:

• event_timestamp_ms  - this is the timestamp at which RevenueCat processed the renewal event. If server notifications are configured for a project (as they are for yours), then the store will typically notify us as soon as the renewal is processed. As you mentioned, the App Store will commonly process a renewal in the final 24 hours of the previous subscription period.
• purchased_at_ms - this is the timestamp at which the newly renewed subscription period begins. You'll commonly see this set to a few hours after the event_timestamp_ms for the reasons described above.
• expiration_at_ms - this is the timestamp at which the newly renewed subscription period will end/expire (unless renewed again).

Here’s a reference to the early renewal processing in Apple’s documentation:

During the 24-hour period before the subscription expires, the App Store starts trying to renew it automatically. The App Store makes several attempts to automatically renew the subscription over a period of time but eventually stops if there are too many failed attempts.