Usually when you get this login error message, it is because the Zumpul installation wasn’t completed properly, most of the time because is needed to enable an API on your Domain.

TO FIX ANY installation Error on Zumpul and enable the API, please follow the next 1,2 and 3 steps:

1. Go to https://admin.google.com and login with your Super admin account. 
   
   
2. Go to this link and Make sure the API access is enabled as is on this image https://admin.google.com/AdminHome?hl=en#SecuritySettings:flyout=apimanagement
   
   
   
   
   
   
3. Reinstall Zumpul from this link https://z.aeegle.com/onInstall