Not sure if it may provide the answer, but perhaps check your online Sonos profile country settings and see if they are incorrectly set to United States…

https://www.sonos.com/en-us/myaccount/user/profile

My Sonos web profile language is set to en-CA and my address is set to Canada. 

Is there another place to indicate country?

Not that I am aware of, perhaps it’s the Alexa App, or something on the Amazon side of things, but if you can’t resolve it, it may maybe best to first reproduce the issue, then immediately submit a Sonos system diagnostic report from within the Sonos App, note it’s reference and then contact/chat with Sonos Support via this LINK to discuss the matter in detail and see what the Staff can perhaps then suggest to resolve the matter.

I don’t use Alexa.  I can see in the Sonos setup process for Amazon Music where it attempts to sign-in to Amazon/US to make the connection.  Of course Amazon/US doesn't know anything about me because my Prime account is at Amazon/CA.

I will give your suggestion a try.

Thank you.

C.

Is the native Amazon Music App on your device, or the Amazon account linked to a US Amazon account in some way, perhaps? I suspect the Sonos App is getting the Amazon store details from something installed on the mobile, (another Amazon App), but that’s just a guess,