In Caterbook, every payment or refund has an ID that relates to the booking, in the format P-XXXX-N.
P- means this item is a payment/refund.
XXXX is the booking reference number.
-N is the numbered payment for this booking.
P-1132-1 would be the first (deposit?) payment for booking 1132.
P-1132-2 would be the second (final balance?) payment for booking 1132.
In Caterpay, each transaction has a transaction cross reference that you can use to find it in the Merchant Management System, or similarly if you have a transaction you are querying from the MMS, you can copy the XREF and search Caterbook for it.
This can be found in Payment reconciliation under the Finance tab. Click through to the relevant date using the blue link icon at the head of each column.
and search based on the booking reference (eg #1132) or Transaction Ref.
Any transactions showing in red on this report, as seen below, are transactions that did not successfully complete.