Every merchant has a contract with secupay, or even multiple ones for different purposes. The API offers an object called General Contract to access the contract. The awkward details are managed behind the scenes by our system. What's important is that you will receive one or multiple General Contract IDs (GCR_xxx) and information how to use them. You need to manage to use the right contract ID for the right purpose.
The Payment Transaction manages the payment process between secupay and your customer, as well as between secupay and you, the merchant. It is defined by the payer and the payee, the payment method and the amount, and if needed a number of options.
A Smart Transaction manages a business transaction, like a purchase order for instance. If this includes one of our payment or loyalty services, it also manages the life cycle of the Payment Transaction or Loyalty Transactions. Furthermore it manages the checkout process, and can track the fullfilment of an order.