Hey @milan@social.tchncs.de, I'm seeing a weird issue with your server that means all the Android clients I've tried (Pachli, obviously, but also the official Mastodon app, Megalodon, Trunks, and Tusky), can't login.
During the login process they're not redirected to the .../oauth/authorize endpoint, so the app never has a chance to get the necessary tokens to complete authentication.
More details in https://github.com/pachli/pachli-android/issues/210
Other servers running Mastodon (e.g., mastodon.ie, mastodon.social) are not affected