A developer token is associated with a production manager account, not a test manager account. You need to create a
production manager account and then follow
these steps to sign up for API access. You'll be granted a developer token with test access which can be used to make API requests against your test accounts. You'll need to get your developer token approved by filling out this
form. After token approval, you can start using your developer token to target your production AdWords accounts.
Shwetha, AdWords API Team.