Opencart v2 Worldpay relay response error - php

Question

Any guidance/advice would be great.
We have WorldPay installed with Opencart 2.0.1.1
All online orders/transactions work fine, everything processes.
However, at the end of the transaction the relay response does not work.
Customers are not re-directed back to the website.
WorldPay have confirmed this should be working (all settings are correct)
It must be a problem with the worldpay.php itself.
Complete shot in the dark, but has anybody experienced this? Opencart forums are usless.
Really appreciate your help!
<?php
class ControllerPaymentWorldPay extends Controller {
private $error = array();
public function index() {
$this->load->language('payment/worldpay');
$this->document->setTitle($this->language->get('heading_title'));
$this->load->model('setting/setting');
if (($this->request->server['REQUEST_METHOD'] == 'POST') && $this->validate()) {
$this->model_setting_setting->editSetting('worldpay', $this->request->post);
$this->session->data['success'] = $this->language->get('text_success');
$this->response->redirect($this->url->link('extension/payment', 'token=' . $this->session->data['token'], 'SSL'));
}
$data['heading_title'] = $this->language->get('heading_title');
$data['text_edit'] = $this->language->get('text_edit');
$data['text_enabled'] = $this->language->get('text_enabled');
$data['text_disabled'] = $this->language->get('text_disabled');
$data['text_all_zones'] = $this->language->get('text_all_zones');
$data['text_yes'] = $this->language->get('text_yes');
$data['text_no'] = $this->language->get('text_no');
$data['text_successful'] = $this->language->get('text_successful');
$data['text_declined'] = $this->language->get('text_declined');
$data['text_off'] = $this->language->get('text_off');
$data['entry_merchant'] = $this->language->get('entry_merchant');
$data['entry_password'] = $this->language->get('entry_password');
$data['entry_callback'] = $this->language->get('entry_callback');
$data['entry_test'] = $this->language->get('entry_test');
$data['entry_total'] = $this->language->get('entry_total');
$data['entry_order_status'] = $this->language->get('entry_order_status');
$data['entry_geo_zone'] = $this->language->get('entry_geo_zone');
$data['entry_status'] = $this->language->get('entry_status');
$data['entry_sort_order'] = $this->language->get('entry_sort_order');
$data['help_password'] = $this->language->get('help_password');
$data['help_callback'] = $this->language->get('help_callback');
$data['help_total'] = $this->language->get('help_total');
$data['button_save'] = $this->language->get('button_save');
$data['button_cancel'] = $this->language->get('button_cancel');
if (isset($this->error['warning'])) {
$data['error_warning'] = $this->error['warning'];
} else {
$data['error_warning'] = '';
}
if (isset($this->error['merchant'])) {
$data['error_merchant'] = $this->error['merchant'];
} else {
$data['error_merchant'] = '';
}
if (isset($this->error['password'])) {
$data['error_password'] = $this->error['password'];
} else {
$data['error_password'] = '';
}
$data['breadcrumbs'] = array();
$data['breadcrumbs'][] = array(
'text' => $this->language->get('text_home'),
'href' => $this->url->link('common/dashboard', 'token=' . $this->session->data['token'], 'SSL')
);
$data['breadcrumbs'][] = array(
'text' => $this->language->get('text_payment'),
'href' => $this->url->link('extension/payment', 'token=' . $this->session->data['token'], 'SSL')
);
$data['breadcrumbs'][] = array(
'text' => $this->language->get('heading_title'),
'href' => $this->url->link('payment/worldpay', 'token=' . $this->session->data['token'], 'SSL')
);
$data['action'] = $this->url->link('payment/worldpay', 'token=' . $this->session->data['token'], 'SSL');
$data['cancel'] = $this->url->link('extension/payment', 'token=' . $this->session->data['token'], 'SSL');
if (isset($this->request->post['worldpay_merchant'])) {
$data['worldpay_merchant'] = $this->request->post['worldpay_merchant'];
} else {
$data['worldpay_merchant'] = $this->config->get('worldpay_merchant');
}
if (isset($this->request->post['worldpay_password'])) {
$data['worldpay_password'] = $this->request->post['worldpay_password'];
} else {
$data['worldpay_password'] = $this->config->get('worldpay_password');
}
$data['callback'] = HTTP_CATALOG . 'index.php?route=payment/worldpay/callback';
if (isset($this->request->post['worldpay_test'])) {
$data['worldpay_test'] = $this->request->post['worldpay_test'];
} else {
$data['worldpay_test'] = $this->config->get('worldpay_test');
}
if (isset($this->request->post['worldpay_total'])) {
$data['worldpay_total'] = $this->request->post['worldpay_total'];
} else {
$data['worldpay_total'] = $this->config->get('worldpay_total');
}
if (isset($this->request->post['worldpay_order_status_id'])) {
$data['worldpay_order_status_id'] = $this->request->post['worldpay_order_status_id'];
} else {
$data['worldpay_order_status_id'] = $this->config->get('worldpay_order_status_id');
}
$this->load->model('localisation/order_status');
$data['order_statuses'] = $this->model_localisation_order_status->getOrderStatuses();
if (isset($this->request->post['worldpay_geo_zone_id'])) {
$data['worldpay_geo_zone_id'] = $this->request->post['worldpay_geo_zone_id'];
} else {
$data['worldpay_geo_zone_id'] = $this->config->get('worldpay_geo_zone_id');
}
$this->load->model('localisation/geo_zone');
$data['geo_zones'] = $this->model_localisation_geo_zone->getGeoZones();
if (isset($this->request->post['worldpay_status'])) {
$data['worldpay_status'] = $this->request->post['worldpay_status'];
} else {
$data['worldpay_status'] = $this->config->get('worldpay_status');
}
if (isset($this->request->post['worldpay_sort_order'])) {
$data['worldpay_sort_order'] = $this->request->post['worldpay_sort_order'];
} else {
$data['worldpay_sort_order'] = $this->config->get('worldpay_sort_order');
}
$data['header'] = $this->load->controller('common/header');
$data['column_left'] = $this->load->controller('common/column_left');
$data['footer'] = $this->load->controller('common/footer');
$this->response->setOutput($this->load->view('payment/worldpay.tpl', $data));
}
protected function validate() {
if (!$this->user->hasPermission('modify', 'payment/worldpay')) {
$this->error['warning'] = $this->language->get('error_permission');
}
if (!$this->request->post['worldpay_merchant']) {
$this->error['merchant'] = $this->language->get('error_merchant');
}
if (!$this->request->post['worldpay_password']) {
$this->error['password'] = $this->language->get('error_password');
}
return !$this->error;
}
}