SSO OAuth Keycloak - Unexpected Application Error

Hello everyone,
I am currently trying to set up a Single Sing On via the command-line interface; specifically Keycloak.

The following link leads to the description for setting up an SSO service for TTN/TTI: Single Sign-On | The Things Stack for LoRaWAN

As described in the example, I used the following command to set up Keycloak and adjusted the parameters accordingly:

$ tti-lw-cli authentication-providers create goog \
--allow-registrations \
--configuration.provider.oidc.client-id \
--configuration.provider.oidc.client-secret GOCSPX-Vxxxxxxx \
--configuration.provider.oidc.provider-url \
--name Goog

On the login page I now also see the Keycloak button, but unfortunately I get an Unexpected Application Error after clicking on it!

Bildschirmfoto 2024-04-12 um 14.51.45
Bildschirmfoto 2024-04-12 um 14.51.58

The login via Keycloak works perfectly with other applications with the same credentials. Google also works without any problems. Do any of you already have experience with Keycloak?