Thank you for using Apple Support Communities! I understand that you are encountering a billing error for your Apple Music subscription. I would be happy to help point you towards a resolution.
Here's a resource that could help:
If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store - Apple Support
When you update your payment method, the iTunes or App Store will automatically attempt to charge you for any unpaid balance. To view your purchase history, and see the amount of an unpaid balance, check out the steps in this section:
Pay an unpaid bill
On your iOS device: Go to Settings > [your name] > iTunes & App Store, then tap your Apple ID. Tap View Apple ID and sign in with your Apple ID, then tap Purchase History. (You can also view your purchase history in iTunes on a Mac or PC.)
Find the unpaid purchase, which is likely at the top of the list, and tap it, then change your payment method.
If you're still encountering the error after following the steps in that resource, contact Apple Support using the link here:
Get more help
If you still need help, contact Apple Support.
Take care!