I have a number of stations in my favourites and they are working fine. 
What steps have you tried, to get it working? Try deleting and then re-enabling MyTuner. 

Hi, I've deleted cache of the app then uninstalled it and rebooted my phone. Installed app again, added MyTuner Radio back and searched for stations. UK stations work nearly all but German, Czech, Slovak not even one. I try to play straight from the search or to add them to my favourites but nothing helps so far.

Sonos is doing nothing otherwise I guess it would have been already sorted. On Yamaha receiver platform to make MyTuner Radio working, I have to pay I think £3 a year. I don't mind it with Sonos though. Their speakers have brilliant sound 

Have you contacted MyTuner? 

No haven't tried that. All problems started with Sonos update in March 2024 or May 2024..

If you are in the UK you may be suffering from georestrictions that seemed to happen in Spring. I can’t now find the exact article that explained why at least some foreign stations are blocked in the UK.
 

Some have had success defining custom urls in the TuneIn app and favoriting there. They’ll then show up in Sonos in the TuneIn (New) service.

Follow these instructions if you want to try that method:

https://support.sonos.com/en-us/article/use-tunein-to-add-internet-radio-station-urls-to-sonos

You can find some stations’ urls e.g. in this website:

http://fmstream.org/index.php?c=FT

Earlier post discussing similar:

I’m in the UK and the only work around I found is to tell Alexa to open my tuner radio and then tell it to play the radio station you want. Weirdly it won’t work on the app (Sonos or Alexa)

This answer was really helpful, thank you, and the key is the site with the streaming URLs. Thanks to you I’ve now, despite the best efforts of the Sonos exec broligarchy, got my favourite US public radio stations back across the house, much appreciated.