Open cart buy now button clearing all my cart data when I use buy now button?

I have integrate buy now extension in my open cart web app. When I click buy now it works perfectly but it clear all my cart data. Open cart version is 2.2 and I have integrate huntbee extension. Here is the url for the buy now extension. http://ift.tt/1XDWQ34

How can I solve it. Anyone please help me. Thanks in advance.