OptionalamountOptionalAuthOptionalcavvOptionalclientidOptionalcurrencyOptionaleciOptionalErrOptionalHASHOptionalmdOptionalmdOptionalmd1 means the card was fully authenticated
OptionaloidOptionalProcSet by the bank when it charged the card (3d_pay, 3d_pay_hosting)
OptionalResponseOptionalstoretypeOptionaltaksitOptionalTransOptionalxid
Fields EST POSTs to okUrl / failUrl.
HASH(ver3) covers every other field.