Paypal IPN Transaction ID's

Question

This is probably fatigue setting in, but I am a little confused about the use of Transaction ID's in IPN transactions.

I understand that PayPal assigns a transaction ID and POSTs that back with all the other gumf. However, it also states that a single transaction may generate more than one IPN message (i.e. as the payment status moves from PENDING to CONFIRMED). In which case more then one message witht he same transaction ID may be received.

My confusion is around all the samples provided (by PayPal themselves as well as PayPalTech). Every script I have seen only processes the first message received via IPN - if the transaction ID already exists (especially when writing IPN transactions to a database), then it is effectively ignored.

If this is the case, are they not potentially missing out on those transactions which start PENDING and then become CONFIRMED?

Am I missing something or just making this more complicated than it needs to be?

Answer 1

The additional transaction ids are generated when for example you're funding the purchase using a credit card. So then there's one TransId for charging the CC, another TransId for sending the money to the receiver. But the receiver only sees "his" TransId, not the CC-related. So there will always be one TransId returned. The Transaction Id is not changed when the status of a transaction is changed (pending/confirmed, etc).