Can't login to iTunes Match
I'm trying to download my iTunes library so I can close my iTunes Match account but I'm unable to add my computer. I don't remember ever having removed my current mac from my Match account but, when I opened up Music to download my tracks I realised that I had to add to add it again.
Trouble is, when I click the 'Add this computer' button, nothing happens. And nothing happens for quite a while. The button greys out... but that's it.
Any thoughts? I've tried authorising and de-authorising the account.
(Late 2012 iMac running Catalina 10.15.7)
iMac 27″, macOS 10.15