Hi,Payment gateway expert and already implemented many payment services into various shopping cart including Interspire(Big Commerce).Please take a look at my reviews. I have been through your requirement and understood that you need a Direct/API integration and for this you need to install SSL(https://) I hope you already installed SSL on your server. Please provide integration manual from 3rd party provider. I also need FTP and site admin login details. After completion,I will send you all the files as zip,so you can use/re use it in future. Hope to hear from you and looking forward to work with you. Thanks!