I think that is the challenge for Alex. He either has to produce a PP confirmation, or move on from this probation request which I am assuming is dead already.
But I think at the 6-month mark (or something reasonable), I would have come to an agreement this was not going to happen. Two years has led to confusion if a payment was ever even made or not.
It is rather easy to confirm in Paypal whether a payment has been made or not. Just click on "Payments sent" then just pick the time period you want. For example, I just checked on all of the payments I sent between 9/1/08 and 12/31/08. If Alex did in fact make a payment to Jon through Paypal, he should be able to find it in about 2 minutes. Of course, Jon could do the same thing but by clicking "Payments received" instead.