You might have an outstanding bill. If these links don't help, contact iTunes Store support directly.
If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store - Apple Support
https://support.apple.com/en-us/HT203005
Change payment method to None; stop requests to verify payment method
https://www.igeeksblog.com/how-to-stop-verification-required-when-installing-fre e-apps/