If you're using an older version of Bambora's module, you need to remove it before following the instructions below. Click here to see how you remove the module
Log in to your Shopify administration.
Click on Settings -> Payments
in the menu.
Scroll to 'Alternative payments', and choose 'ePay / Payment Solutions' from the dropdown menu (see image 1).
Enter your merchant number in the field "Merchant number". Find your merchant number on your Bambora administration in the menu Settings -> Payment system
Enter your Shopify key in the field "Shopify Key". Find your Shopify key on your ePay administration in the menu Settings -> Shopify integration
Press 'Activate' (see image 2).