I haven’t seen your landing page, but I’m betting it’s got some kind of problem. Have you tested it on mobile devices and multiple desktop browsers? How’s the load time?
Beyond the obvious technical stuff, you’re going to have to look at your web visitor stats to see if there are more clues. A high bounce rate, for instance, can suggest a number of things (slow load time, poor design, content that’s not interesting enough).
If you’re sure that your server and content are in top shape, then look next to your sales process. It’s got to be a one-click, low-impact buy. Simplify and shorten this process any way you can. If it’s longer than one click, then make your landing page into an opt-in page with as few fields as possible. Lots of opt-in fields will chase people away. We suggest a name and email address only, and possibly a password if you’re creating a personalized on-site account for each visitor.