Offline Payments

When a customer chooses one of our offline payment methods, it looks like they get sent to our payment gateway (sagepay) momentarily then returned with a 'payment declined notice' on the last stage of the checkout.

The order comes through to us fine but this is going to be confusing for the customer.

We use v3 of CS-CART. Where are the settings or code for what happens when the order is submitted using an offline payment method or how do i resolve this issue?