If you're reading this you probably can't download apps because your iphone or ipad says "Paypal not a valid payment method; please verify your account"
After sifting through lots of online speculation I found the answer. This is what fixed it for me. I had to go into the setting icon, select "icloud" then click on "account" which should match your itunes account name, re-enter a valid credit card and save, close out. Go onto your itunes on your desktop, go to "view account" then edit payment method. Enter the same credit card you just entered on the iphone under the icloud section. Go back to the phone and see if you can download apps.
Hope it works for you!
