Typical amazon support - and they are unlikely to have a clue tbh. They’ll not have heard of Wiim, they’ll tell you it’ll only work with echos etc etc. You may be lucky and get a techie who will understand what WiiM/Linkplay devices are, that they have been developed using Alexa’s MRM API and that they do support AlexaCast from the Amazon Music app. It might be worth a call but my experience in dealing with them is often frustrating, long winded and ultimately pointless - yymv hopefully
Btw, in the alexa app where you can see your WiiM device, can you long press on some music on the play page and select your Wiim there? Also, can you use the blue “talk to Alexa” icon and ask something like “Alexa, play Born to Run on Wiim-device-name”? That would at least show that it’s recognised as a device that can play music and perhaps point to issues with the amazon music app and not the Wiim device itself.