I would send a support request in on that one as staff would have to help you if it is a backend issue or help out if the payment had problems. Make sure you give them as much detail as you can and provide them with a copy of all information you have from paypal about your payment.
In my experience with paypal, sometimes payments are listed as “pending” until the funds clear. Why this is, I don’t know. Sometimes my payments go through immediately and at paypal it will indicate “completed” and sometimes it takes a few days and will say “pending.”