How do I sign in when already a customer?

And now you have a recommendation of an affirmation to do what is clearly outlined in the link I provided in the first response I made.

The link does indeed say this, "...make sure that you're signed in to all of your devices with the Apple ID that you use with Apple Music."

I guess some people think you are incapable of reading a link, or maybe they just don't read links themselves to see what they contain :-/

Limnos wrote:

I guess some people think you are incapable of reading a link, or maybe they just don't read links themselves to see what they contain :-/

Neither. I had opened the post before your reply was visible, and I took a bit too long to answer and post it. Next time I'll remember to refresh the page to see if there are new posts while I did something else.

You log in with the Apple ID that holds the subscription to iCloud and iTunes & App stores on your device.

Turn on [/off] iCloud Music Library with Apple Music - https://support.apple.com/HT204926

As was just indicated in the affirmation of what I posted earlier, just sign into the Music service with your Apple ID.