How do I uniquely identify a BlueSnap transaction using the IPN parameters?

Question

Support informed me that this is impossible, but I highly doubt that any payment gateway skips providing such important information.

I've read the docs and wasn't able to find anything of use. In my mind, the candidate for the unique identifier is the suspiciously named referenceNumber parameter, but again, the docs don't tell anything useful about it.

How does one uniquely identify these IPNs?

Answer 1

The referenceNumber is indeed the transaction number (or Order number) and is unique in the BlueSnap (Plimus) system.
That said, a transactions has a lifecycle (order placed, delivered, refunded, etc.), so you may get several IPNs with the same referenceNumber. These can be differentiated using the transactionType field.