Whenever you need to add a Merchant gateway, you will need this "configure" option to set up your new merchant's configuration. The Configure option looks like as shown below. 

You will need to click on the "Edit Icon" to select your chosen merchant on the list or you may also "request to add a merchant" that you can't find on the list.

NOTE:  To request adding a merchant not included in the list, you may email us @ support@nexusmerchants.com