Have you followed the instructions found here?:

https://support.sonos.com/en-us/article/share-your-macos-music-folder-with-sonos

Hi Thanks for the responses.  I’m sorry for the late reply but have had a very busy couple of weeks.  I have tried the above and no luck.  I get as far as adding in the Music Libarary but the add button is greyed out. Any idea what I could try next.  I did check that the Firewall was not the problem

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.