Android app Expected 'https://' in custom server

New user. Installed app. Registered for an account. Tried to login but got the following error:

Expected ‘https://’ in custom server

I don’t know what is a “custom server”.

I have successfully logged in via the web but am not able to do so via the app.

Custom server refers to a self-hosted installation. If you’re not running your own server, then leave that field blank to have the android app use the setup that most people use.

Thank you for the reply. As noted in my post, I am not able to get logged in via the app so please let me know how and where I would leave what blank.