Payment Module Set Up
Next step is to set up payment handling. For this to happen, you will need a merchant account with a payment handler, e.g. 2checkout.com, ClickBank.com or PayPal. If you already have one, please locate the Payment link under the Modules icon in the administration index page of your osCommerce and click it.
A list of payment options will appear. These are all included in the default osCommerce, but you need to install a module in order to be able to receive payments.
Installation is easy. Just select the vendor you have an account with your mouse pointer and click the Install button.
When installation is complete, you will notice that the symbol 0 appears on the row. In the rightmost column two buttons will appear: Remove (self-explainable) and Edit.
Clicking the second button will allow you to insert your merchant account details, set your preference for e-mail notifications, etc.
There are two important choices that have to be made: one is the Transaction Mode and the other one is Sort order of display.
The Test transaction mode can be used for checking whether the payment links are correct or when your store is offline. It is important to switch to Production mode once your store goes live.
Sort order of display refers to the payment handler preference: the lower the number - the higher the preference for the particular module, with 0 representing top choice. When done click the Update button to save your changes.