Allowing users to enter only listing

I'd like to set Directory up where if a user signs up, they can enter ONE free business listing.

I thought it would be possible to do this by enabling 'credits' where the user it would need 1 credit to list, and the user gets 1 free credit on sign up. Do I need to change anything else? Because, it doesnt seem to work, when a customer tries to list, it takes them to the payment page (no free first listing).

Thanks