Found the solution - it works if QR code is scanned via Control Center and not via Camera!!

Same issue. Not able to login / purchase.

No, I don't think its possible. ( I understand that you want to automatically detect which user did INITIAL_BUY)

As per the link you shared, only "REFUND" notifications will be sent for all types and not others (the ones you tried in sandbox are INITIAL_BUY). And afaik you can't try REFUND in sandbox :(

Afaik, the user has to reach out to Apple support to do this and it cannot be done from Developer side. (Apple doesnt have something like Order Management)

the expiration date wont be present under "receipt". It will be present under "receipt.inapp" (which will have an array of all subscriptions).