PayPal associates a Transaction ID to each transaction. You can use the Transaction ID to track the status of transactions, or to search transactions.
Transaction ID is a 12-character string of printable characters, for example:
Printable characters also include symbols other than letters and numbers such as the question mark (?). A Transaction ID typically contains letters and numbers only. Also, Payflow uses the term “PNREF” when referring to Transaction IDs.