Book Online & Payment System

[eluser]Aken[/eluser]
Your client will need to sign up for a merchant account in order to be able to accept credit cards, then you'll need to integrate it somehow. Depending on what merchant account you use, some will have code libraries available to use, others you'll need to integrate entirely on your own. There's a lot to it, very hard for someone to sit here and tell you everything you'll need.

I suggest doing some research into how the payment process behind e-commerce works, see if you can find how some people have integrated various merchant accounts with CodeIgniter, and go from there.