Hi Xlttx,
A step you can try as it's saying information is missing, is to ensure the information for your Apple ID is correct and fully set up before adding a payment. Log into Manage your AppleID or try Settings > [Your Name] > Name, Phone Numbers, Email and check to make sure all of your information is correct including your name, birthday, phone numbers, and emails.
If it needed to be updated, try again. If it didn't, try updating your payment method on a different device. Change, add, or remove Apple ID payment methods.
Hope this helps.Have a good day!