Did you recently subscribe to Apple One?
Is Apple One still in the Free Trial phase?
Did you cancel your stand alone Music subscription before subscribing to Apple One?
If the answer to all 3 questions questions is yes, then your Apple Music subscription is currently inactive and will not reactivate until the Apple One Free trial is over and you are charged for it the first time.
There was no need to cancel your stand alone Apple Music subscription when subscribing to Apple One. It automatically transfers. If you cancel the stand alone subscription, then you can not access it during the Apple One free trial.
See the "What is included with Apple One" section in the link below.
click here ➜ Bundle Apple subscriptions with Apple One - Apple Support