I need to connect OpenCart to Bank of America Merchant Services which uses FirstData/PayEezy:
https://merch.bankofamerica.com/global-gateway-e4-features
I'm guessing I need an extension for that? Do you know which one?
Take a look around the Opencart Marketplace and you can find extensions to add FirstData support to your opencart site. Using one of those would allow you to not have to figure out FirstData's API.