This article is for the error:
It seems you tried to log in with a user that does not have Google Ad Manager enabled. Please try again with another user account.
This means that your Google account has not been properly set up to access Google Ad Manager or API access was not enabled yet. Please check with your System Administrator to make sure the account you are using has the correct permissions to access this. See also General Data Source Access Requirements for more information on what is required for your account.
There also is a specific account setting for API access that must be enabled for Supermetrics to be able to connect. Under Admin->Global Settings->Network Settings, there is a small tick box to allow API access. This must be checked.