Allows to identify if the transaction is part of a series of payments (subscription or payment in installments).
Useful for accurately identifying the first payment of a series.
With the application of Soft Decline, the payment gateway automatically makes a new payment attempt with 3D Secure authentication, when possible. This changes the payment sequence number. The vads_sequence_number field no longer allows to easily identify the first payment of a series.
Output field, returned in the response (IPN and Return URL).