Keycloak - SSO - UMC Portal not working

last week i installed and configured Keycloak for external access as descriped at 8. Use cases — Univention Keycloak app manual 23.0.7

When i login at the umc with sso (keycloak) the login is working and i can see all the tiles.
When i click on a tile for example on “Users” i get the error message “Session timed out… not authorized”


I installed keycloak on a backup server.
The portal and single-sign-on url ( is pointing to the same server where keycloak is installed.

Are there any hints for troubleshooting?

External Access for Microsoft 365 is working.