One of the supported payment modes: 1 - Paypal, 7 - Paypal Sandbox, 8 - Moneybookers, 11 - WorldPay, 12 - WorldPay Test, 13 - Authorize.net, 14 - Sage Pay, 15 - Sage Pay Test, 16 - MultiSafepay, 17 - MultiSafepay Test, 18 - EBS, 19 - Servired, 20 - Servired Test, 21 - Authorize.net - DPM, 22 - Mastercard MiGS, 23 - Wirecard QPAY, 24 - Paybox, 25 - Mercanet, 26 - SystemPay, 27 - SystemPay Test, 28 - CC Avenue, 29 - DIBS, 30 - DIBS Test, 31 - Cobrebem, 32 - Cobrebem Test, 33 - Be2Bill, 34 - Be2Bill Test, 35 - Checkout.fi, 37 - Montrada, 38 - DIBS Flex, 39 - DIBS Flex Test, 46 - CMCIC, 47 - EWay, 48 - EWay Shared, 49 - Sherlock, 50 - Authorize.net CIM, 51 - Authorize.net CIM Test, 52 - Coinbase, 53 - Ogone, 54 - Saferpay, 55 - 4Cs, 56 - Stripe, 57 - Paylib, 58 - PayPal Payflow Pro, 59 - PayPal Payflow Pro Sandbox, 60 - Przelewy24, 61 - Checkout.com, 99 - custom payment gateway (use this value if implementing your own payment gateway as per FAQ Q231)