Issues with in app paypal purchase

I want to make an in-app purchase from an app I’ve purchased from before, and it tells me I need to verify payment method in iTunes. I click paypal and went through all the steps, come back and it tells me I need to complete the form. All the information is correct, so I click done then it tells me the paypal account already exists. Can’t make a purchase! There are no issues with paypal or my card information.