iTunes account creation not allowed when trying to test In-App Purchases

Solution 1:

Looks like Apple has this poorly documented. Basically, you shouldn't log in with your sandbox user from that screen. Log in when actually prompted by your test IAP.

Source: Unable to log in with sandbox test users on device

Solution 2:

I just had the same problem. Here's how I solved it:

1. Don't try to sign in Settings > iTunes & App Stores
2. Log out of iTunes & App Stores (make sure you're not logged into any account)
3. Just open the app you're trying to test
4. Your app will promt you to sign in
5. Enter your credentials for your sandbox test account

Et voilà! You're done. Worked for me. I hope it works for you.

Solution 3:

For those who are still facing an issue, here is the solution: From settings main screen, select "iTunes & App Store", as seen in the picture

now scroll to bottom and you will find your previous apple is still there, sign out of that, see picture for reference, and now when doing in app purchase, it will ask for both apple id and password, use your sandbox tester apple id and password there.

Solution 4:

I had this issue. I tried changing existing Sandbox tester account password and tried to login on device...but didn't worked.

Even iPhone device restart didn't worked [last option that most developer follows ;-) ]

I thought it takes time to update this newly created Sandbox testing on DB. So left the login option as it is on device

Now, after launching app that contains In App purchase. Press on button that is responsible for In App purchase. This will prompt for Apple credentials. Enter the Sandbox tester credentials here.

Voila this worked for me!