The unique identifier for a transaction which also match the UniqueID in our merchant console (BIP) is the processorIdentifier.


We have two additional identifiers in the mobile.connect (ios and android SDK system).


The identifier 
"transaction":{ 
"identifier":"1c078a968e9b4be1a909c80dd8acf2ea", 
is for a group of transactions (e.g. a refund would get the same identifier as the initial debit transaction).


The subtransactionIdentifier 
"subTransactionIdentifier":"f09a58f2b5e44b57a9272bd1a81cdfbe", 
is a unique identifier for every transaction in our system (e.g. different for the refund and initial debit transaction).



Sample Response being used in answer above:


{
"event":{
"identifier":"b61b1a5c-27cc-415d-b51f-9999c97a5303",
"type":"transaction.succeeded",
"created":"2013-06-13 09:54:13"
},
"transaction":{
"identifier":"1c078a968e9b4be1a909c80dd8acf2ea",
"subTransactionIdentifier":"f09a58f2b5e44b57a9272bd1a81cdfbe",
"customIdentifier":"",
"transactionType":"DB",
"paymentMethod":"CC",
"amount":30.00,
"currency":"EUR",
"subject":"My subject",
"processorIdentifier":"ff8080814472f0a80144730a33481d88",
"mode":"LIVE"
}}