Can't sync local lan server from flatpack app

Operating system

Linux

Joplin version

3.0.15

Desktop version info

Joplin 3.0.15 (prod, linux)

Client ID: 533865cfc1d546e7acac162c256f537b
Sync Version: 3
Profile Version: 47
Keychain Supported: No

Sync target

Joplin Server

What issue do you have?

Hello. I have flatpack version installed on Linux Mint and I have local lan server on Docker running on http://myserver.local:22300
I'm able to get to server over web browser and I'm able to set synchronization on my iPhone. But when I try it in Linux app I get:

Error. Please check that URL, username, password, etc. are correct and that the sync target is accessible. The reported error was:
request to http://myserver.local:22300/api/sessions failed, reason: getaddrinfo EAI_AGAIN myserver.local (Code EAI_AGAIN)

I'm confused because it's working on iOS and I clearly can connect via web browser so server is visible. Login and password are correct I triple checked it.