The integration between Sonos and Amazon can sometimes throw up annoying, confusing and sometimes completely random issues.  A very large proportion of these issues can be resolved by some very simple tasks.  These have been documented across multiple posts and have remained fairly consistent since the functionality was released.  However, some of my earlier posts are now obsolete due to changes within the navigation and terminology of both the Sonos and Alexa Apps.  As a result, I have compiled an updated set of steps to help users resolve the most common issues.  However, before we start please don’t get phased by the scale of the steps below, they are not all required!  I have tried to list these with the most common and easiest solutions first building to a complete reset.  But before we start, if you are experiencing issues with Alexa, then please check for any outages on this page first: Sonos Status

If Alexa is not responding but has in the past, please ensure that the mic hasn’t been turned off by accident – just touch the Mic symbol to toggle the mic on and off.

Before we delve down to various resets, please open the Sonos App>Settings>Services and Voice>Amazon Alexa and ensure that your device is shown as Enabled – if not Enable.

Please Retest.

Duplicate device names – Although Amazon states that Alexa has the ability to know the different actions for different device types, my experience is Alexa prefers that names for Devices, Groups and Scenes are unique,
1.1/ Please open up the Alexa App and press the ‘Devices’ button in the bottom right of your device.  You’ll need to make a note of any duplicate names, a common mistake is to have a Room and a Device with the same name. I personally use the naming standard Room Name + Device type. e.g. Kitchen Sonos, Kitchen Echo Dot, Bedroom Sonos, etc. Although this would appear to make the voice control of devices more complicated, the use of Groups, removes the need to name these specific Device names in most voice commands.  Here is a link to my naming standards: https://en.community.sonos.com/amazon-alexa-and-sonos-229102/best-practices-for-naming-of-devices-6819283/index1.html;
1.2/ You can then change them in the source app. e.g. Use the Sonos App to change the name of Sonos players.
1.3/ In the Alexa app, select the Alexa Icon in the centre of the row of Icons at the bottom of the screen and ask ‘Alexa, Discover Devices’.

Please Retest

Account Linking - 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 one 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/ If you have multiple Amazon accounts logged into different Apps on your device, this can confuse the Amazon Authorisation. Please ensure that you log out of all Amazon related Apps and 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 at least 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'
Please Retest

Duplicate IP Address – Please see my Post here: en.community.sonos.com

Please Retest

Edit: Updated.

Also, can you confirm your location.

I had decided last night to take the sonos back so I packed it away. I then read your guide above and decided to give it one last chance. Plugged it in and it worked straight away!!……so thanks for the tips above but didn’t need them. what i’m really annoyed about is the fact i didn’t change anything from last night so a glitch somewhere that inevitably will appear again. :-) 

In that case, I’d check the last link for duplicate IP addresses.