Defining the steps of the payment process - As seen by the merchant

Here is what the online payment process looks like from the merchant's point of view:

Figure 1. Payment process - as seen by the merchant

The buyer validates the shopping cart.
The merchant website creates a form using the data from the buyer's cart.
The merchant website redirects the buyer to the payment gateway. The redirection is done via an HTML POST form using HTTPS. The parameters of the form are described in the chapter Generating a payment form.
After the buyer enters the payment method details, the payment gateway proceeds to the payment.
Depending on the shop settings (see chapter Setting up notifications), the payment result is automatically transmitted to the merchant website.
The merchant website analyzes and processes the payment result.
It updates the database (order/stock status, etc.).
The buyer sees the payment result on the payment gateway. If the buyer decides to return to the merchant website, he/she sees a "thank you" message and the order status appears.