This is a know issue and has had a number of posts with accepted solutions. Have a look here’;

And here:

I am not a technophobe; therefore, can somebody please give me step-by-step instructions on how to perform this? I am desperate to get my music back. Thank you.

HB

The two posts above yours have links to detailed explanations. 

I have read quite a bit about the answers to the problem. There is a suggestion that I am strongly encouraged to create a new user on Windows, especially for sharing. Should I do this or is it unnecessary? Before I carry on, I would like this answered first. Thanks.

How to Setup SMB File Share on Windows Super Fast in 10 minutes (themakersphere.com)

HB

It shouldn’t matter, unless you are concerned with security.  I’ve used both a Sonos specific user and the default for my NAS over the years.  The only thing that’s a pain is I tend to forget the Sonos user password, so I’ve had to go in and wipe it a couple times. 

Okay, I don't know how I did it, but in the end, after a further Sonos update, it accepted my music folder. This is for the room I spend most of my time in. Now, I have to do it in another room where I spend less time. You would think now that I've done it in one room, it should be easy for me. However, I am disabled, and to get it to work in the room I spend less time in is trickier than you think. Anyway, I now have an idea about how to fix it. Thanks for all your help in directing me to the correct existing answers, jgatie. I'll let you know how I get on with the other PC in the other room when I'm next in there.

HB

I didn't know how to edit the above post so I have just posted another. Just to let you know, I have now got my music back in the other room too. Phew!

HB