[freeside-users] Registration Code Usage

[webmaster]

I have one question about the One-time registration code, is this another way for payment? If yes how can I use it?
In fact I want to create prepaid cards for a selected package, for example when a user enters its prepaid card number, the signup server directly picks its package, I want to prevent the users form selecting the package. I think we have to use the Registration code!
Thanks for your help
Sameh Fakoua