付款方式在cs购物车中无法正常工作

I create a new payment gateway in cscart. After get success result from payment gateway cs cart redirect it to checkout page and show incomplete checkout.Please help me to solve this issue.

Because you did not provide any code, I made an example code for processing the response:

if ($mode == 'return') {
    // this means, that the payment processor returned from 3rd party checkout page

    $order_info = fn_get_order_info($_REQUEST['order_id'], true);

    // you should have a response code (this section depends on your payment gateway)
    if ($_REQUEST['response_code'] == "S") {
        // the transaction was successful!
        $pp_response['order_status'] = 'P';
        $pp_response['transaction_id'] = $_REQUEST['transaction_id'];
        $pp_response["reason_text"] = $_REQUEST['response_code'] . ": " . $_REQUEST['transaction_id']);


        fn_finish_payment($_REQUEST['order_id'], $pp_response, false);
        fn_order_placement_routines('route', $_REQUEST['order_id']);
    } else {
        // the transaction was NOT successful!
        $pp_response['order_status'] = 'N';
        $pp_response['transaction_id'] = $_REQUEST['transaction_id'];
        $pp_response["reason_text"] = $_REQUEST['response_code'] . ": " . $_REQUEST['transaction_id']);

        fn_order_placement_routines('route', $_REQUEST['order_id'], false);
    }
}

The key "functions" are: fn_finish_payment() and fn_order_placement_routines(). If you did not finish the payment, you will be redirected to the checkout page, because this means, something went wrong.