Need experienced Authorize.net API programmer to fix problem

I have a online store that uses a Digishop shopping cart version 8. I was ready to launch it today with [login to view URL] as my payment gateway which is already installed into the cart, but when I hit the submit button for a order the cart just goes to a blank screen and doesn't process the payment. I talked to [login to view URL] and they told me that my shopping cart is not connecting to their gateway for some reason and needs to be fixed. So, I need someone with [login to view URL] payment gateway API INTEGRATION experience to figure out what's wrong and fix the problem. I'll provide the store url in PM after you tell me your qualifications. EXPERIENCED WITH [login to view URL] PAYMENT GATEWAY ONLY!