Hi ​@sweatyjock, welcome to the Sonos Community!

I’m sorry to hear that you’re having issues signing into your Amazon account on Sonos. Just for a bit more information, are you failing to sign in while adding Amazon Music or are you failing when trying to add Amazon Alexa? 

I’d recommend trying a different device with the Sonos app installed if you haven’t. It’s also been noted that uninstalling the Amazon Shopping app can help with finalizing the setup of Amazon Alexa (this could also be true for Amazon Music).

If you try the above and are still having issues, then I’d recommend contacting our support team for further troubleshooting assistance. 

I hope this helps!