invoiceninja/app/Ninja/PaymentDrivers/PayFastPaymentDriver.php

<?php namespace App\Ninja\PaymentDrivers;

use Request;

class PayFastPaymentDriver extends BasePaymentDriver
{
    protected $transactionReferenceParam = 'm_payment_id';

    public function completeOffsitePurchase($input)
    {
        parent::completeOffsitePurchase([
            'token' => Request::query('pt')
        ]);
    }
}