You can append your own additional customer specific transaction information values to the continue/return URL or the cancel URL.(Any name-value pairs embedded in the URL should be URL-encoded to ensure correct processing in the form request.) This customer specific information will be passed back to your server, where you can use it to identify the specific customer and transaction that has been processed, when the customer returns. However, as these setting values are used to obtain a token, which is then used to request a secure form to process a transaction, the Transaction Id, doesn't exist at the time when your name-value pairs were submitted.
In addition to or as an alternative you can use Webhooks.
