Unable to play purchased music

For reasons that have been forgotten tears ago I have music purchased under two different Apple IDs. It has not been a problem in the past, I simply authorised new devices to play music from both accounts.

Now I can only play tracks from my primary account. When I attempt to play those on the secondary account I get a message (on my Mac, the tracks in the secondary account dont appear in the same playlist on my iOS devices) saying 'This computer is not authorised to play...' prompting me to enter the password for the secondary account. Having done so I get a 'There was a temporary problem completing your request. Try again later'. No further error info.

I have tried logging out of my primary account in Apple Music and logging into the secondary one. I dont get any errors but the account doesnt appear in the Account menu as it should.

I can log into the secondary account on the Apple ID website so I know log in details are correct.

I have subscribed to Apple Music with my primary account in the hope that it would know to that it would be covered under that subscription but that does not work.

The only solution I have found is to find the track in Apple Music and add to the playlist. The downside of this is that I have many (hundreds?) of tracks I bought with this secondary account. Also I would need to continue the Apple Music subscription - effectively paying twice for the same music...