That’s a Play:5 2nd Gen.  The firmware may be too far out of date.  Connect it to your router via an Ethernet cable, then try to add.  After it adds and updates, you can then deploy it wirelessly. 

Agreed with @jgatie . I have a couple of these as well.

And if you can’t get it updated by wiring it directly, it’s worth a call to Sonos Support directly to discuss it. I’ve needed to do so before with a device that had an OS that wasn’t able to be updated. Took them a minute or two to provide me a link with which I was up and running within 5 minutes. 

Not that it matters, but isn’t it an old Play:3 ?

OK, you forced me to get up and go look at both. You’re right, this is a PLAY:3, and not a PLAY:5 gen 2. 

However, the rest of @jgatie ‘s post stands, as does mine. :)

Ugh, you are correct.  That’s what I get from relying on memory after age 50.

Sorry, what was it I posted here ?  ha ha 

That’s definitely a Play:3 - I use a pair as surrounds with my Arc. I’d suggest you do a factory reset on it, then add it as a new speaker to your setup.

https://support.sonos.com/en-us/article/reset-your-sonos-product

Unless you have moved from S1 to S2 or S2 to S1 for some of your units, this should be straight forward.

If the PLAY:3’s were working six months ago this is not an ancient firmware issue. In all of the construction confusion you may have rearranged your network. Before Factory Reset, I recommend wiring the PLAY:3’s to the network. I expect that they’ll figure things out. In the process they will update, if necessary, to match the other units. Once they are working, you can deploy them as before.

Thank you for all the suggestions. I got it up and running. I reset it and was able to connect it to Sonos System. 

Thank you