The unique transaction identifier.
This property will contain the Base-64 encoded TransactionId value received in the response to a Payer Authentication Request (PAReq).
Note: Some payment processors require the TransactionId (XID) be submitted in a 28-byte Base-64 encoded format. If so, the value contained within AuthenticationXID can be sent. If the value should not be sent Base-64 encoded, the value specified within TransactionId can be sent.
This property is read-only and not available at design time.