Stuck on "you can approve this ipad from one of your other devices"
My ipad running iOS15 wants me to update Apple ID settings. Asks for my password - I enter it. OK. Asks for my iPad passcode - I enter it. OK. And then it says "Enter Passcode for Other iPad" and asks for the password I use to unlock my old iPad "Strathmore" - I enter it. But then it says "Verification Failed, there was an error verifying the passcode of your ipad." This continues indefinitely. If I try to get out of it by clicking "Forgot iPad Passcode" it says I can approve this iPad from one of your other devices signed in to iCloud.
I have many devices signed in to iCloud, iOS and Mac, but I can't figure out any way they will let me approve my iPad. If I open iCloud in another device, I'm all logged in, there's no window saying Approve ipad. I can generate a 6 digit verification code on my other devices, but the iPad provides no place to enter that code. How do I get past this?
iPad Pro, iPadOS 14