First question has to be: having reset your speaker, have you gone through setting it up again on your system? Did you then reinstall Alexa service on the speaker? 

Also, can you open the Sonos App and select the cog wheel in the top right hand corner, then select ‘Manage’.  Scroll down to ‘Voice Assistants’ and check if Amazon Alexa is listed.  If it is, please select it and then select ‘Add to another product’.  Please follow the prompts on the App from there.

If this doesn’t work, or if Amazon Alexa is not listed under ‘Voice Assistants’ above, then please remove the Sonos skill within the Alexa App and try adding Alexa to Sonos again.  Please come back to us if the problem persists.

Edit:

For anyone else reading this post, this is a good example of the reason to not factory reset your device unless recommended! 

Seems like a load of people are all having the same issue with this. No what you say to do does NOT work. Also, you’re kind of being a d*** with the nerd emoji taunting me that I “reset” it when MAYBE I’m a new owner of said unit and it was sold to me this way. Not even gonna bother with it, forums are all correct in that your company  does not give a *  about the issue, reaffirmed by your * attitude.

*Moderator Note: Modified in accordance with the Community Code of Conduct.*

Seems like a load of people are all having the same issue with this. No what you say to do does NOT work. Also, you’re kind of being a d*** with the nerd emoji taunting me that I “reset” it when MAYBE I’m a new owner of said unit and it was sold to me this way. Not even gonna bother with it, forums are all correct in that your company  does not give a * about the issue, reaffirmed by your * attitude.

*Moderator Note: Modified in accordance with the Community Code of Conduct.*

I'm just a Sonos user, not employed by Sonos. I'm a little confused by your reaction, as I'm just trying to help you resolve your issue. Perhaps, it would be best if you contact Sonos support.

https://status.sonos.com/