This was the issue I had.  I've spent quite a bit of time on the phone and by email with support.  In the end I got it working but the Sonos app always reported there was a problem.  I removed all sonos from alexa, logged out of all amazon apps and tried to add again from Sonos.  As always it reported there was a problem. But I noticed that in the Alexa app 2 of my units were showing as online and 2 as offline.  I tried to play music through the online ones and it worked.  I went back to the sonos app and it was now showing these as with Alexa but I had to change the settings to turn on the chime.  For the other two I had to power cycle and add 1 at a time. In each case sonos reported a problem but alexa showed online and then could play music or voice command and they would appear in the sonos app shortly after.  It could take a couple of goes but eventually worked. I have reported all of this to support.  All units have been working  fine since. 

Not sure if this helps at all. But maybe worth a try.

I only have the one unit - a Sonos one. I was able to enable the skill in Alexa but it shows the device as offline in my Alexa app. However, I’m able to play music on it from the Sonos app. 
 

How do I proceed?

if it showed offline I needed to try again.  I could only get it to work when the Alexa app showed as online  even though the sonos app reported a problem adding Alexa.  

Update: I have played with every option. I have now added Alexa back into the voice section of amazon Alexa. I disabled the Sonos skill in the Alexa app and even deleted the speaker to connect again. Everything shows up as connected now. 

However, Alexa doesn’t function properly on my Sonos one. I’ll give my echo Commands and it carries it out. When I activate Alexa on my Sonos one, it doesn’t know date/time or even my address for location. 

Can you just check that the small light round light is displayed on the top of the Sonos One.  If not the Mic is been switched off accidentally, just tap the mic symbol to toggle back on.

The mic is on. Example: I have a smart thermostat that I frequently have Alexa change the temperature on. When I ask Alexa to do so, she says “sorry I can’t find a device called ‘AC’”. My echo and the Alexa app handle this task normally. It’s strange because the Sonos one used to be able to do all these things without any issues. 

Can you check for duplicate Devices/Groups within the Alexa App?  Also, have you booted your Router recently?

No duplicate devices or groups. I can reboot my router now. 

Okay, I rebooted the router, reset my Sonos to factory settings, reset the Sonos app, deleted everything from the Alexa app and readded it. 
 

I can’t control any of my smart home devices and I’m not able to use Alexa to play anything from Spotify. I’m only able to use the Sonos app to play music on my Sonos One. 

Okay, it’s never a good idea to reset your Sonos device but… Have you Enabled the Sonos skill in the Alexa App? If you open the Sonos App>Settings>Voice & Services>Amazon Alexa do you see your Sonos One Enabled?

I have. It shows as enabled and the device appears as a speaker in the Alexa app. 

Is the small white round light still shown on the top of the Sonos One (Just touch the Mic symbol to check - it will toggle on and off)

Yes it is. The response is either “sorry I didn’t find a device named ___” or “sorry there was a problem.”

Can you power off and on your Sonos One and then ask 'Alexa, discover devices.'

“I couldn’t find any new smart home devices. Please enable the smart home skill in the Alexa app.”

The skill for my Honeywell thermostat is enabled in my app. If I ask my echo spot to change the temperature, it works. But not if I ask my Sonos.

Can you submit a diagnostic and post the number in this thread?

I’ve been having same issue since upgrading to S2. I initially disabled and re-enabled and couldn’t link. Tried again this time retyping Sonos email and password (not allowing iPhone to auto fill) this worked and now linked ok. Still can’t get Alexa to work tho. Says sorry “kitchen is offline” 

any clues?