I have an Amazon music unlimited subscription which I can play through my Sonos set up. For example I played the Who's Quadraphenia in its entirety yesterday along with tracks from the Eagles, its just now and again when I ask Alexa to play certain tracks it plays a sample rather than the whole track.
This was posted by Ryan S on the Sonos Community forum and re-posted here with his kind permission.
Ryan is obviously based in the US as the currency is in dollars and the link in page here is for the Amazon US site but his solution is sound.
There is an Amazon Music Unlimited Echo Plan which is $3.99/mo and the Amazon Music Unlimited Individual Plan, at $7.99/mo. These prices are per the page here. The Echo Plan only works on an Echo, Dot, or Tap. They don't work with the Sonos One which is not an Echo device. You'd need the Individual Plan to to play some tracks. If you have Prime, it'll play many songs through Prime Music, without Unlimited. But some songs would play those short clips as a sample.
Can you check your subscription to make sure which level you're listed at?