In case of 3-D Secure payment, contains the context of the transaction retrieved from the cardCheckEnrollment method. In case of 3-D Secure server Standalone, it contains the Payer Authentication Request (PAReq) that the merchant must transmit to ACS for 3-D Secure authentication (format: base 64 encoded).In case of external payment provider, contains the context of the transaction sent by the merchant during the transaction initialisation.