ลองทำตามนี้ดูนะครับ  จาก reddit

NEW SOLUTION January 17th 2020.

I just got off the phone with Apple support and they guided me through the solution. It worked right away after struggling with google a reddit for an hour. Step by step:

Settings. Click on your name. iTunes and App Store. Click Apple ID. Sign out.
Force close all apps.

Settings. Scroll down to music. Make sure Show Apple Music is toggled on. Press Join Apple Music. Since you are signed out it will ask you to purchase. Just purchase the free trial. Enter Apple ID and password. Confirm. Password again. Once you do this it will tell you that you are already a member.
Force close everything. Go to settings. Music. Turn on Sync Library. Pay attention to the next question. Keep music or not. Whatever your preference.
Force close it all again. Go to Music app. Library will be syncing but you can search an Apple Music song and play to confirm it works. You’re welcome.
I saw all the posts and trouble people have been having so I had to share. Enjoy.

Trefry