Oauth2 login leads to "Not Found" in Authentik

[merentitis]

Describe the bug**

Login attempt with Autehntik as Oauth2 Provider seems to fail.
It leads to a 404 on my idP.
Get result:

GET https://auth.example.com/application/o/authorize?client_id=myid&redirect_uri=https://booked-staging.example.com/Web/oauth2-auth.php&scope=openid email profile&response_type=code
Status 404 Not Found

To Reproduce**

Steps to reproduce the behavior:

1. Go to Login page
2. Select "Login with Oauth2"
3. Redirected to Authentik and get 404

Expected behavior**

Authentication should succeed

Screenshots**

Additional context**

Authentik is working with other services.
Librebooking config:

 'oauth2.login.enabled' => true,
            'oauth2.name' => 'OAuth2',
            'oauth2.url.authorize' => 'https://auth.example.com/application/o/authorize/',
            'oauth2.url.token' => 'https://auth.example.com/application/o/token/',
            'oauth2.url.userinfo' => 'https://auth.example.com/application/o/userinfo/',
            'oauth2.client.id' => 'myid',
            'oauth2.client.secret' => 'mysecret',
            'oauth2.client.uri' => '/Web/oauth2-auth.php',

Authentik additional info:

Redirect URIs: https://booked-staging.example.com/Web/oauth2-auth.php
OpenID Configuration URL: https://auth.example.com/application/o/booked/.well-known/openid-configuration
OpenID Configuration Issuer
https://auth.example.com/application/o/booked/

Specifications

Latest Docker version v4.0.0