Allow Spotify through whitelist on Firewall - no covers loading

[neoinfantilism]

Hi,

I allowed spotify for my kids on the router's firewall (Fritz Box), adding spotify.com on the whitelist of the router.

Everything works fine, except the covers that are not loading. It works if I allow any url, but that's exactly what I want to avoid.

Can you tell me the url where the spotify app gets the covers from, so I can add them to the whitelist?