this is not a valid matrix server address

#### Describe the bug
There is red text at settings -> general -> home server.
Last line. Below is retry button.
"this is not a valid matrix server address"
I have no idea what is wrong. Pretty much everything is working. Except some voice call problems. Can't receive calls with some phones if the screen is closed. But that's different thing.
If I hit the retry button, it does something and text comes back.

#### To Reproduce
Steps to reproduce the behavior:
1. Go to 'settings, general, home server'
2. See error

#### Expected behavior
It would be nice to know what is wrong. We need a better error description.

#### Smartphone (please complete the following information):
- Device: Samsung S10+
- OS: Android 11

#### Additional context
- Element 1.1.6 - F-Droid
- Homeserver installed with this guide. spantaleev/matrix-docker-ansible-deploy