If you log into 2 checkout you will need to got to the link that says "Account" then "site management" you will need to fill out all information the first box needs to be checked that says "on"

once all is completed click save test your checkout via your website, like you are a customer and at the end you will not get that message. if you are using a demo until your website is reviewed and approved you will not be charged as a matter of fact no one will, until you are approved.

make sure that you get your account number that is located in your 2co area and in the same section "site management" get your secret word. and place that in your information area in the payment module section within your zencart.

Problem i have is when i tested it out all seemed ok until the last step i get a blank page from the process_2checkout.php.

If you get that then i dont know what to do unless i do the same post it on here. but you will get an error 406 at end.