Books asks me to validate a payment method on iPad but not iPhone or Mac

Hi folks,

Until two days ago I would buy, download and read books on my iPad (series 7); now I'm asked to verify a payment method and verify my iCloud password even though, I have already purchased the book in question. Whatever I do, I can't get past these dialogues.

My payment method is valid and allows me to make purchases on my other devices. I added an alternate payment option, PayPal, also valid, but the problem persists.

However, I have no issues, reading the purchased book on my iPhone and Mac. Each of my devices are linked to the same AppleID, I only have one.

Any insight would be gratefully appreciated.

Mike