Old Apple TV authentication problem - won't verify Apple ID

I am trying to enable the remote app control on an old Apple TV. It claims my Apple ID is incorrect, and I am getting login confirmation notifications on my iPhone, but I can't get the Apple TV to show me the verification screen.

Back story: I have set up an old TV in my office and found an old Apple TV unit. Not sure which generation but its previous to 4K (thinner unit, same basic design). Problem is: no remote. I have a couple of other remotes which I have tried to pair with it, but it doesn't work.

I have managed to get it going anyway, by restoring it using my Mac. Still won't recognise my other remotes. But I have connected a keyboard and used that to try to enable the remote app. It asks me to enable Home Sharing, then enter my Apple ID login details. At that point I get a notification on my phone, but the Apple TV says the login was incorrect and won't take me to the screen where I can enter the verification code.

Any suggestions how I can get past this? I have tried a restart. Would there be any point in another restore ( the firmware was updated when I did the previous one)

Thanks

Dominic