Follow these setup instructions to register the unofficial Overcast service on your Sonos system.
From the iOS Sonos App, go to Settings > About My Sonos System. Check out this Sonos support article if you're on another platform.
Enter your Sonos IP here and click Register Service. The window on the right should say
success! if the service was successfully installed.
Alternatively you can run this
curl command in the terminal.
From the iOS Sonos App, go to Add Music Services and find Overcast in the list. Log in with your Overcast.fm email address and password.