Enter passcode for other ipad?

After updating my ipad air, there is a nag about update apple id settings. I enter my apple id and password, and then I'm presented with a popup saying Enter passcode for other ipad that is expecting 6 characters.

The only other ipad I have is an old ipad 2 that is used as a display for a weather station. It doesn't have a passcode, and even if I were to enable passcodes on it it only accepts 4 digit passcodes. The popup doesn't accept 4-digi passcodes (I tried setting a passcode on the old ipad and using that passcode in the popup, but it doesn't let me pass).

I just installed icloud on my pc, although that helped absolutely nothing - although I get the are you logging in from (location 2500 km away from where I am sitting) and the 6-digit code I need to enter to access the website icloud.com on the ipad air.

This seems pretty hopeless. Should I just chuck the ipad and buy a samsung tablet instead?