Always, always, always do a test purchase prior to any launch.
This will ensure that the integration (PayPal, JVZoo, etc.) is working properly. If there are any issues, check your settings. If everything looks fine then submit a help desk ticket for us to investigate.
Note: If you are using Hostgator then chances are your test purchase will fail. Hostgator has some unique mod security rules that block the IPN data from hitting MemberSonic.
We can walk you through the process of getting Hostgator to whitelist the rules if need be.