"Can't assign these applications to your account".

When trying to update my MAC apps via the App store, I get a prompt to sign in with my AppleID, which I do, but then I get a message saying 'Your request is temporarily unable to be processed.'

followed by "Can't assign these applications to your account". This is exasperating, as I'm on a deadline. Any suggestions gratefully welcome: 2015 MAC Book Pro, running OS 10.14...