Android app can't add a server: sign-in completes, returns to the app, and no server appears

App 2.7.3 against server 2.14.5. Adding the server opens the URL, I sign in, it hands back to the app, and the server simply is not there — no error, and app debug logging produces nothing. Clearing app data and reinstalling from a different source changed nothing. The server log shows failed to get redirect response TypeError: fetch failed with [cause]: [Error: URL scheme must be a HTTP(S) scheme].

Resolution: The cause is an authentication layer in front of Storyteller, not Storyteller itself: when the reverse proxy enforces its own SSO/forward-auth on the Storyteller host, it intercepts the OAuth-style callback that hands the session back to the app, and the redirect to the app's custom URL scheme never completes — which is what the URL scheme must be a HTTP(S) scheme error is reporting. Disable the proxy-level SSO requirement for the Storyteller host (Storyteller does its own authentication) and the app adds the server immediately. Check the whole chain, since a proxy can enforce this at more than one layer and the login page itself may still render fine. Do not try downgrading the server to a version that once worked — there are one-way data migrations between 2.13 and 2.14, so you cannot go back without restoring a backup.