Below is the information that extracted from "Gateway Implementation Guide v4 1 5 - 2013-01-07.pdf". No special trick, just follow the document.

MERCHANT_KEY
  GROUP_ID 
  SECUREKEY 
  SECURENETID 

CARD
  CARDCODE 
  CARDNUMBER 
  EXPDATE 

INSTALLMENT
  AMOUNT 
  AUTOCALC_OPTION (A—automatic M—manual)
  BALLOON_AMOUNT (Balloon amount)
  BALLOON_OPTION (AutoBill offers the capability of the balloon payment to be applied to the first or last payment, as following: 0 - add balloon amount to first payment 1 - add balloon amount to last payment)
  COUNT (Number of total installments for installment plan.  1-99.)
  REMAINDER_OPTION (AutoBill offers the ability to choose first or last payment if installments are not equally divided, as following: 0 - add remainder to first payment 1 - add remainder to last payment)


RECURRING
  AMOUNT (Total value to be charged to the payment method specified.  Include decimal point followed by decimal amount.) 
  NOEND_FLAG (0 = Recurring bill has an end date; 1 = Recurring bill has no end date)


OPTIONS
  CYCLE 
  DAY (Required if CYCLE=M, Q, B, or Y)
  FREQUENCY (If CYCLE=M: 1 – 11 (i.e. 2 = every 2 months))


PLAN_AB (This object defines the information that can be submitted to the Gateway for AutoBill transaction processing.)
  CUSTOMERID (Contains customer ID associated with payment plan. It cannot be a valid card number.)
  INSTALLMENT
  MERCHANT_KEY
  PAYMENTID (SecureNet Vault Payment ID.  Must be enabled on the account.  It cannot be a valid card number.) 
  RECURRING
  SCHEDULE (Array of PAYMENT_AB)
  STARTDATE (Plan start date. MMDDYYYY.  Verify the date is on or after current date.) 
  TYPE (Using the “Recurring AutoBill” payments can be scheduled for daily, weekly, monthly, quarterly, and yearly recurrence.Set TYPE to one of the following: REC—for recurring INS—for installment VAR—for variable.)


TRANSACTION
  MERCHANT_KEY
  CARD
  CHECK
  CUSTOMER_BILL
  CUSTOMER_SHIP
  ENCRYPTION
  LEVEL2
  LEVEL3
  MPI
  AUTO
  PETROLEUM
  HOTEL
  PRODUCT
  SERVICE
  USERDEFINED
  SECONDARY_MERCHANT KEY
  TERMINAL
  HEALTHCARE
  IMAGE