What should happen: i should be able to add music/url etc
what happens: console spams with this error and overlay doesnt open:
log:https://paste.ee/p/LI7nF

player version: Music-Player-1.0.0-2
core version:U-Team-Core-1.12.2-1.1.2-60
minecraft: 1.12.2
forge: 2705

I can't reproduce this.
Your mentioned stacktrace is from u-team-core but this doesn't affect the musicplayer.
java.lang.IllegalStateException: IPCClient (ID: 427196986064764928) is not connected!
I'll fix this the warning reporting in the next u-team-core update.

But the musicplayer should work nevertheless. Have you tried this?

Closed because no response and not reproducible