Spotify: correctly installed, but no control possible

For almost two years, I have been trying to get the Spotify integration to work without success, I use a paid service. The service is displayed correctly, and I can also see in the tile which devices are currently available as sources. I use a Denon AVR X1300w, which can also be controlled via the Denon integration.
But: when I open the Spotify tile, it shows unavailable or inactive. Even if I set the correct destination manually or via a script. The correct song is sometimes displayed, but the controls do not work, here the error message media_player/media_play no active media device found appears.
After having tried many approaches, I am wondering if my spotify username could be the reason: it starts with a #