Have you sold anything using paypal? If no, then don't worry. Just tell PayPal that you have received money for posting the the PTP forums. You are providing the posting service and they are paying you. there is no such written agreement, so how can you provide documents. If they still want to verify, they should contact the people who have sent you money.
Friend, yesterday I called paypal but I just lost Rs. 300. They put most of the time the call on hold and I haven't got any proper answer as to how I can unlimit it.