Yes, I have exactly the same issue as onlyoneme.
Alexa app sees WiiM Mini device and recognizes my Amazon Music subscription. Alexa app can cast to the WiiM Mini.
The Amazon Music does not see the WiiM Mini device.
I am EU resident (PL) - I suppose the issue persists because of a country issue (Amazon Music subscription is linked to PL, but the Alexa may not be linked to PL).
I can cast to the three different Chromecast devices that are active in my home network from within Amazon Music app.
Alexa app sees WiiM Mini device and recognizes my Amazon Music subscription. Alexa app can cast to the WiiM Mini.
The Amazon Music does not see the WiiM Mini device.
I am EU resident (PL) - I suppose the issue persists because of a country issue (Amazon Music subscription is linked to PL, but the Alexa may not be linked to PL).
I can cast to the three different Chromecast devices that are active in my home network from within Amazon Music app.