Can't sign in to iCloud, due to error verifying phone passcode

Hi guys

Having a lot of fun with this Catalina update... the latest problem is that I can't fully sign in to my iCloud account because, when I get to the part where I have to enter the pass code off my iPhone it says 'There was an error verifying your passcode'.

I have tried this several times, after resetting etc and it still comes up with the same result. I thought it might be asking for my old iPhone passcode but this didn't work either and I have since taken that phone off the iCloud.

Anyone know of a fix?