I have just managed to resolve this issue with technical support as a workaround until the permanent fix is deployed and the steps are as follows:

Using an iOS Device from a Friend, Relative or Neighbour.

1. Connect their device to your Wi-Fi network.
2. Download the Sonos App
3. Download Apple Music (if not already downloaded)
4. On the iOS Device click Settings > Their Apple ID > Media & Purchases > Sign Out
5. Launch the Sonos App
6. Click Join Existing System
7. Login to your Sonos ID
8. Click on Apple Music in the Sonos App
9. Click Re-authorise
10. Follow the journey in Apple Music.
11. On the iOS Device click Settings > Their Apple ID > Media & Purchases > Sign Out

Then your Friend, Relative or Neighbour can sign back into Media & Purchases. Finally uninstall the Sonos App