Hi @Chezparrs
Welcome to the Sonos Community!
Do you even see YouTube Music as an option to add in Services & Voice » Add a Service? If not, please sign in at https://www.sonos.com/login and go to Profile to check you country is correct - if it is not, please update it and allow 24 hours before adding the service for the change to take effect.
If your country is correct, and you see the option to add YTM, but it just doesn’t work, I recommend you reboot your router by switching it off for at least 30 seconds. It will take a few minutes for WiFi to return - I suggest you reboot your phone too while you wait. Trying from another device may also help.
If you are still unable to add the service, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.
I hope this helps.