There is currently a snackbar in the login for errors. Just signed out and typed in a wrong password to make sure I didn't break anything. However, I am on version 0.0.19. If you downloaded the app from F-Droid, you're on the first public build. I'm still trying to get another update out from the initial release.

I've added a new ticket linking back to this comment and I'll look into the issue. I have several people using Syphon with their own homeservers successfully so I'm thinking the problem has to do with a silent error that's unrelated. Thanks for the feedback though and feel free to respond in the github issue itself.