I'm using TestFlight to test an app with payment/subscription functionality. I created sandbox accounts in AppStore Connect accordingly to be able to test the subscriptions. I'm logged in with the sandbox account.
When I try to subscribe in the App the wrong account (this is my actual real AppleID) is used for the subscription although it is recognized that this is just a sandbox subscription.
I tried:
logging off/on into the sandbox account
creating a totally new sandbox account
trying to trigger the payment with no logged in sandbox account
The result is always: in the payment popup it is stated that the purchase account will be my original AppleID and not a sandbox account.
How can I switch the accounts? Is this a bug at Apple's side somehow?