Are you using a VPN? Can you check the Device Location for your Sonos devices on the browser version of the Alexa App. Also, please check your Sonos Profile for the correct location.
Thanks for the tips!
On alexa.amazon.com I can see two entries for each sonos device. I belive that the other one represents the “sonos as a speaker” and the other one represents the “alexa enabled device”. All of the “alexa enabled device” are offline on the list.
The location cannot be changed for the speakers because they are just speakers; On the other hand the location cannot be changed on the alexa devices either because they are ‘offline’.
Sonos skill is enabled on my Alexa and Alexa re-discovers all the sonos devices correctly even if I remove them. As far as I can tell, all seems to be working on the Alexa-end of things.
This leads me to think that there is something wrong at the Sonos App -side. This is a very curious problem since previously (only 3 weeks ago) I still was able to remove and add Alexa successfully to all my speakers.
...and P.S. I don’t use VPN
Can you power off the Sonos devices for about 5 secs and then see if they come back online? If yes, please try again.
If not, please see my article: Tips & Tricks - Resolving random issues impacting Sonos devices.. | Sonos Community
Tried powering of for 5s and longer too. And did a factory reset on two speakers too. No luck 
But found out a solution too! 
It’s quite a tedious workaround for this matter. I disconnected all speakers and reset my Sonos mobile app (ios). Then after re-launching the app, I went on to create a whole new sonos system. Now when I add the speakers, it allows me to add Alexa too as usual.
If someone else tries this approach, I’d advice to remove all Sonos devices and disable Sonos -skill on Alexa too before proceeding.
Hi @Sikantti
Welcome to the Sonos Community!
I am glad you found a resolution, though it was a bit extreme. Should you run into this problem again, I recommend you get in touch with our technical support team, as it seems likely all you needed to do was de-register the Sonos devices in your Amazon/Alexa account.
The same thing happened to me when I removed an arc from my account to re-add it connected to a new TV. The solution is to de-register the Sonos device from your Alexa account. Then you can Add Alexa to it in the Sonos App.
I've tried all the above and still can't get it working. I was on to support via chat earlier who got me to check location in my profile was right and we did a full reboot all round and no joy. I just tried starting a new Sonos system and it's still the same error. 
