I'm migrating my app to Store Kit V1, to Store Kit V2, and, due some legacy circumstances I'm implemented in past using a synchronous method, calling verify receipt on my server to validate receipt and do the needed business logic, but due to the deadline I changed the entire app integration and some questions starting to appear in my mind.
First of all, when I processing the purchase when basically I will receive the notification? When the Store Kit calls the transaction.finish or after the purchase was successful I always will receive this notification?
App Store Server Notifications are triggered server-side when events take place due to direct user action (e.g. purchases, changes in renewal product preference) as well as due to background processes (subs expiring, renewing, etc.). Regardless of what triggers these events, the appropriate notification is sent to your server a short time after they take place. The sending of notifications is distinct from StoreKit and the state of the transactions on the user's device. So for your question of a purchase - once a user successfully completes a purchase, the App Store Server will trigger the appropriate notification (e.g. SUBSCRIBED/INITIAL_BUY) to be sent to your server shortly afterward, regardless of if you've finished the transaction on the device.
To learn more about the different notification types and the events that trigger them, see here: https://developer.apple.com/documentation/appstoreservernotifications/notificationtype
https://developer.apple.com/documentation/appstoreservernotifications/subtype
