Redirection in custom gateway callback

[shetab]

Hi guys.

 

I have implemented a custom gateway in my WHMCS. I want to implement a conditional redirection. So if the payment is the first payment of a new order, redirects to order complemented page and if it is invoicd payment redirect to invoice page. More clearly, if payment comes from cart, redirect to completion page otherwise, invoice page

 

What do I write in callback script for this?

 

Thanks.