When struggling with App Store payments I always find the Revenue Cat documentation a great go-to resource - https://www.revenuecat.com/docs/test-and-launch/sandbox/apple-app-store#:~:text=Sandbox%20Considerations%E2%80%8B&text=In%20sandbox%2C%20StoreKit%20Test%2C%20and,regions%20set%20for%20devices/accounts.

There's some mention in there of making sure you're on a different / new account. Testing IAP on Apple has always been a nightmare!