Sonos ONE responds to Alexa 'Play' voice commands with 'Undefined'

Hi

I'm using 9.3 and my Sonos One is working fine still. This type of issue is normally down to one of three things:

1/ Duplicate device names - Alexa prefers that names for Devices, Groups and Scenes are unique,
1.1/ Please open up the Alexa App>Smart Home and make a note of any duplicate device names;
1.2/ You can then change them in the source app. e.g. Use the Sonos App to change the name of Sonos players. (I personally use the naming standard Room Name + Device type. e.g. Kitchen Sonos, Kitchen Echo Dot, Lounge Sonos, etc)
1.3/ Once you have changed any duplicate names then please open the Alexa App on a Web Browser(https://alexa.amazon.co.uk or https://alexa.amazon.com)>Smart Home>Devices and select 'Forget All' followed by 'Discover'. NOTE: This will remove ALL Actions from ALL Alexa Routines! (Only the Web version has this functionality.)

2/ Some form of Account Linking or Authorisation has not completed successfully. There are a number of causes for this and it's best to try these steps 1 at a time and test before moving on to the next step if the problem persists:
2.1/ Open the Alexa App>Skills>Your Skills>Sonos and 'Disable' followed by 'Enable';
2.2/ Ensure that you don't have multiple Amazon accounts logged into different Apps on your device, as this can confuse the Amazon Authorisation. If yes, then please log out of the other accounts and then complete step 2.1 again;
2.3/ If the problem still persists, please logout of all Amazon accounts then select the Alexa App>Skills>Your Skills>Sonos and 'Disable. Now power down all Sonos devices for 10 secs, allowing for any wired devices to boot before booting the remaining Sonos players. Now log back into the Alexa App>Skills>Sonos and 'Enable'

3/ If the problem persists then an entire reset of the Authorisation & Account Linking process is required:
3.1/ In the Alexa app, select Skills>Your Skills>Sonos and then 'Disable';
3.2 In the Alexa app (Web Browser version), select 'Smart Home>Devices'. Now select 'Forget All' at the bottom of the screen;
3.3/ In the Sonos app (Android or iOS), select Settings>Room Settings and for each of the Sonos One's sign into 'Voice Services' and select 'Remove Amazon Alexa from this Room';
3.4/ If you have any wired Sonos devices, please power down for 10 secs and then switch on and wait for it to boot;
3.5/ Now power down all other Sonos Players for 10 secs then switch them back on and wait for them to boot;
3.6/ In the Sonos app, Select Manage>Add a player or sub' and add the Sonos One's again. This will complete the set-up process again;
3.7/ In the Alexa app, select Skills>Your Skills and ensure the Sonos skill is 'Enabled', if not please 'Enable';
3.8/ In the Alexa app , select Smart Home>Devices>Discover. Ensure that your Sonos One's are displayed correctly and not shown as 'Off Line'.
3.9/ Also check one last time that there are no devices with the same name. Remember, if there is a need to rename any then you'll need to select 'Discover' again.

Thanks for the response. It got me a step further.

So, this is the problem: I have two households (separate houses). When I re-enable the Alexa Sonos skill, I can only choose one of them. Choosing the household that contains the two ONEs ('System 1' in the screenshot below) fixes the 'Undefined' problem, but then I've lost the Alexa Sonos skill in the other household. Going into 'Settings' for the skill doesn't allow me to add the other household.

Presumably, there is a way around this?

The problem you have is that a Sonos Account is Location (or LAN) specific and the relationship between a Sonos and Alexa account is a 1:1. I would suggest that you create two Alexa accounts and include them in the same Alexa Household and two Sonos accounts, one for each location. If you then link the two Alexa Accounts to the two different Sonos accounts you can then ask 'Alexa, switch profile' when travelling between locations. This should get around this issue.

Thanks for your help. I find Alexa configuration obscure and somewhat poorly conceived compared to most other services I deal with, so I appreciate the expertise.

The problem you have is that a Sonos Account is Location (or LAN) specific ...
That doesn't appear to be generally true: applications using the new Sonos cloud API function correctly with multiple Sonos households/locations per account. Examples include IFTTT and Sonos Menu Bar Controller for macOS, where one just selects the household one wants to target for a particular action.

So, this appears to be primarily an Alexa limitation. Anyway, since I once again need to disable the Sonos Alexa skill for 'System 2' due to the whole-house ducking problem still not being addressed, it's not a pressing issue for me. Perhaps this account mapping limitation will also get addressed in time.

I've had the same problem trying to use Alexa with a Sonos One in one household and a Beam in another household. I finally got around the problem by creating both separate Sonos and separate Amazon/Alexa accounts for each location. It required many log ins/log outs, registerations/deregistrations and device discoveries until it finally, magically worked.

Thankfully, using the same Spotify Premium account works across the two households. I guess that I would be out of luck if I wanted to use Prime Music.

I couldn't agree more with @pwt that Alexa configuration is obscure and convoluted, at least with Sonos. I plan to switch to Google Assistant as soon as it is available for Sonos. I can only hope that the experience is better.

I am having the same issue. I submitted a diagnostic and my confirmation # is 1537817162. When I ask Alexa play x song from Spotify is just responds to “undefined” but I can play music off my phone on it no problem.