This is because the Authorized redirect URI's are not entered correctly.
Ensure the following:
  1. Under Restrictions, enter the Authorized JavaScript origins for the domain of your school's Blackbaud K12 Core (ex., https://yourschool.myschoolapp.com)
  2. Under Authorized redirect URIs, the address entered identifies the route where Google will send responses (ex., https://yourschool.org/api/sso/authresponse?format=html)
NOTE: It is recommended you include two versions: https://yourschool.myschoolapp.com/api/sso/authresponse?format=html) AND http://yourschool.org/api/sso/authresponse?format=html
For the full article and Steps, reference How do I set up Google Apps SSO API?