I think I’d call Sonos Support directly to discuss it.

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

Although it does sound a lot like your phone is unable to resolve the update server’s address. I’d be sure you’re not running any port blocking software, such as VPNs, work profiles, virus protection, or firewalls, too. 

There's no port blocking software on my network, but just to be sure I've tried other networks as well. And why would the Sonos app need access to the update server to add my headphones? 

I'll give Sonos support a call next week, although I might just return the headphones instead. At this point I'm not sure if they're worth the hassle. 

If the Sonos system is going to update the Headphones, it has to get that ‘update’ from the Sonos servers, where the update data lives. If you had any blocking software, that could keep the Sonos system from reaching out to the servers. Since you don’t, there’s something else going on, and calling Sonos would be the right move. 

Have the same problem on my Nord 2 phone incredibly frustrating s o n o s don't seem to care anything ever it doesn't connect to my I have one phone that it connects to for someone unknown reason My phone is barely working