Hello Leon,
the app doesn't support redirects, so you should input the final URL when trying to login in the app.
When you put the URL, the app will always try to connect via https first. If it is unable to connect using https, then it will try with http.
Please check that you don't have any problem with your certificate. You can check it using a tool like this:
https://www.sslshopper.com/ssl-checker.html
Android is more strict with certificates than iOS and desktop.
Cheers,
Dani