Our Photobucket (photo hosting) subscription is due for renewal. I chose to pay by PayPal, but having logged in to the PayPal account via Photobucket's payment page, it wants me to add a credit card to the account 'that will be used if there is not enough balance in the account'. There is a 'skip' button at this point which has no effect. We are a business PayPal user with our account linked to a bank account for funding, so no credit cards involved. I thought the whole idea of PayPal was that one did not enter credit card details.
You are absolutely correct, that is the whole point of PayPal. We are the 'middleman' between you and people you wish to pay. I can only guess that this is a requirement of Photobucket, it's not a requirement of the PayPal checkout flow.
If you are not comfortable giving these details I would contact Photobucket direct as they will be able to explain in more detail.
