This may be due to logging in as a tester before the station is assigned to a username. A new station must be logged in with its original username before a tester username may be used.
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“Station” must be selected as the login type when logging in for the first time, which then “Tester” must be selected when logging in as a tester after previous steps have been done. The image above provides how the login process should look.

You must have a Tester username created prior to logging in as a Tester.