Hi Teyken
Currently the Token authentication flow requires the individual agreements super-user authenticate an app.
When visiting the Request URL you must use the credentials for the SuperUser of the actual agreement. The owner of the individual agreement will have received these credentials in a welcome email when the agreement was created. You as administrator can not install the app with your administrator credentials.
In short the agreements that you administer need to individually follow the requestURL and generate a token.
Please have a look at https://www.e-conomic.com/developer/tutorials step 3(a and b).