This worked but could t find it documented anywhere: in the app go to Account (click on your profile pic at top right-ish), select App Preferences, then Reset App. Afterwards, relaunch app, when it asks if you want to rejoin existing system say yes, then go to System and where device says “Not registered”, click on that, follow the prompts, and this time, it will successfully add. 

SOLVED -   I was having the same issue with AMP and a Move (gen) 1.  I think it is all around their new app.  What I did is go into the app and transfer ownership, it then goes and adds the unregistered items.   Strange but worked.   

Solved! The App reset worked perfect for me and my new Amp, thank you! 

After the update (tonight) it played the sound of my standard tunneln radio ,but did not show my radio and I couldn't control anything.  After reset the app and a lot of trying it says the "boost" is not available (I restarted also that and it shows a white light). The other "play1" are shown , but after reset the music stopped completely  and Now i cannot choose anything.

I also can choose my napster, but pressing play does not work.

  It is always the same After an update, nothing works and no help.  I will never buy that system again

Re: “no help”, before I got this working I tried calling Sonos Customer Care - twice. First call, “your wait time is approximately… 111 minutes”. Tried an hour later, “your wait time is approximately… 105 minutes”. 
 

if I hadn’t stumbled on a fix that works (through trial and error), I would have returned my gear as well. In fact I’m still in the 30 day window, paying attention to issues others are finding. Frustrating for such a powerful system that used to have ease-of-use bragging rights.

If it continues to Fail and not update/register…  https://support.sonos.com/en-us/downloads

Download the Windows/Mac app to your computer (Not the Web App).  You’ll be able to push an update from there.  Then back to mobile device to enter your pin/hit the button, and Done.