Hello Aternos staff!
Could you please add this highly configurable event-based music player to your mod list? It's called ActualMusic. It's needed server-side to properly notify the client about the game-events.
Here's the link: https://minecraft.curseforge.com/projects/actualmusic
And here's the link for it's dependency Embassy https://minecraft.curseforge.com/projects/embassy
Best wishes
Krisu