Approval Link won´t open without valid SOAR User

[MarinusC]

Hello all, 

we are using a Google SecOps Instance and try to use the "Approval Link" Feature for our Playbooks. 
As far as I understand it the approval can also be given from users which do not have an account in the SecOps Instance (First Line "Outside the platform": https://cloud.google.com/chronicle/docs/soar/respond/working-with-playbooks/assign-approval-links-in...)
After the mail is sent to my inbox and I try to open the approve or decline link in Inkognito mode, the screen stays blank and no error message appears. If I open the link in a browser session where I am logged in into Google SecOps, I can approve/decline the question.

Can anybody help me or had the same issue?
I created the playbook exactly as in the instructions mentioned above.

Thanks, 
Marinus