There are a few things that can be causing your purchase not to go through. Below are a few things you can do to resolve this:
If an affiliate link, try purchasing directly from the sales page of the product.
If you're using Google Chrome browser please go to "Settings", Search for "Cookies", go to "All Cookies and Site Data", search for "JVZoo" cookies and delete them. That will get rid of the problem.
For all other browsers a helpful alternative is to clear your cookies in general.
A good free tool to do this is CCleaner ( http://www.piriform.com/download ).
Also clear your browser cache as well and or simply use a different web browser, then try to make your purchase again.
This process will assure that you have cleared any affiliates who may have been cookied in the previous attempts.
If you are still having trouble the issue is with the vendor's account and you will need to direct your request back to them, or PayPal directly.