I shared my Apple Music with a friend and it’s doesn’t working

Ah, okay. They should make sure they're signed in with the same Apple ID as the one you shared with. They should also make sure the operating system they're using is up to date, same with the iTunes app if they're using Windows and Apple Music app on Android. Perhaps even just restarting their device may help solve the problem.

Feel free to let me know how it goes!

Ah, I understand. Has he tried restarting his device and making sure his device's operating system is up to date?

Let me know. :)

What exactly isn't working? Are there any error messages?

Perhaps this article can help you: Get an Apple Music family subscription - Apple Support

In that case, please contact Apple Support. They will be able to assist you and your friend further. (Contact - Official Apple Support)

Have a lovely rest of your day!