Once you have chosen the payment processor which you like to use and registered an account with it, you need to enable a payment module in your OpenCart online store to start accepting payments from your customers.
To add or enable a new payment module in your store you first need to log in your OpenCart Admin area.
Once you have logged in as administrator, go to Extensions » Payments
Select the payment processor you like to enable for your store.
If the module is not installed there will be "[Install]" button on the right end of the selected module's row.
Click the "Install" link.
For this tutorial we will install the AlertPay module.
In order to process your transactions securely most payment processors require you to use a password and a user ID so in this case enter your "Merchant ID" and "Security Code".
The AlertURL must be set in the alert pay client area in order to enable your store to be notified that the payment is completed.
Below you can choose status that the order will have after the payment is completed.
Click "Save" in the upper right corner when you are done editing the settings.
You have already enabled the AlertPay payment module and you are ready to accept payments in your OpenCart store.