Ошибка Unexpected token < in JSON at position 0. Как решить?

При нажатии чека оформления заказа без регистрации, должно выходить заполнение полей, не выходит и после нажатия на кнопку продолжить выскакивает такая ошибка.

Код guest.php

<?php
class ControllerCheckoutGuest extends Controller {
	public function index() {
		$this->load->language('checkout/checkout');

		$data['text_select'] = $this->language->get('text_select');
		$data['text_none'] = $this->language->get('text_none');
		$data['text_your_details'] = $this->language->get('text_your_details');
		$data['text_your_account'] = $this->language->get('text_your_account');
		$data['text_your_address'] = $this->language->get('text_your_address');
		$data['text_loading'] = $this->language->get('text_loading');

		$data['entry_firstname'] = $this->language->get('entry_firstname');
		$data['entry_lastname'] = $this->language->get('entry_lastname');
		$data['entry_email'] = $this->language->get('entry_email');
		$data['entry_telephone'] = $this->language->get('entry_telephone');
		$data['entry_fax'] = $this->language->get('entry_fax');
		$data['entry_company'] = $this->language->get('entry_company');
		$data['entry_customer_group'] = $this->language->get('entry_customer_group');
		$data['entry_address_1'] = $this->language->get('entry_address_1');
		$data['entry_address_2'] = $this->language->get('entry_address_2');
		$data['entry_postcode'] = $this->language->get('entry_postcode');
		$data['entry_city'] = $this->language->get('entry_city');
		$data['entry_country'] = $this->language->get('entry_country');
		$data['entry_zone'] = $this->language->get('entry_zone');
		$data['entry_shipping'] = $this->language->get('entry_shipping');

		$data['button_continue'] = $this->language->get('button_continue');
		$data['button_upload'] = $this->language->get('button_upload');

		$data['customer_groups'] = array();

		if (is_array($this->config->get('config_customer_group_display'))) {
			$this->load->model('account/customer_group');

			$customer_groups = $this->model_account_customer_group->getCustomerGroups();

			foreach ($customer_groups as $customer_group) {
				if (in_array($customer_group['customer_group_id'], $this->config->get('config_customer_group_display'))) {
					$data['customer_groups'][] = $customer_group;
				}
			}
		}

		
		if (isset($this->request->post['customer_group_id'])) {
			$data['customer_group_id'] = $this->request->post['customer_group_id'];
		} elseif(isset($this->session->data['guest']['customer_group_id'])) {

            
			$data['customer_group_id'] = $this->session->data['guest']['customer_group_id'];
		} else {
			$data['customer_group_id'] = $this->config->get('config_customer_group_id');
		}
//lightshop start
		$data['button_back'] = $this->language->get('button_back');
		$data['entry_telephone'] = $this->language->get('entry_telephone');
		$data['entry_email'] = $this->language->get('entry_email');
		$data['checkout_st3_sa'] = $this->config->get('theme_lightshop_checkout_st3_sa');
		
		$this->load->model('catalog/lightshop');
		$activeFields = $this->model_catalog_lightshop->getFields($data['customer_group_id']);
		$allFields = $this->model_catalog_lightshop->getAllFields();

		$data['allCustomFields'] = $allFields;
		foreach($allFields as $field){
			$data['entry_'.$field.'_required'] = 0;
			$data['entry_'.$field.'_show'] = 0;
		
			if (isset($this->request->post[$field])) {
				$data[$field] = $this->request->post[$field];
			} elseif (!empty($customer_info)) {
				$data[$field] = $customer_info[$field];
			} else {
				$data[$field] = '';
			}

			if (isset($this->error[$field])) {
				$data['error_'.$field] = $this->error[$field];
			} else {
				$data['error_'.$field] = '';
			}

		}

		foreach($activeFields as $field){
			if($field['description']){
				$data['entry_'.$field['name']] = $field['description'];
			}
			$data['entry_'.$field['name'].'_required'] = $field['required'];
			$data['entry_'.$field['name'].'_show'] = $field['is_show'];
		}
//lightshop end
		if (isset($this->session->data['guest']['firstname'])) {
			$data['firstname'] = $this->session->data['guest']['firstname'];
		} else {
			$data['firstname'] = '';
		}

		if (isset($this->session->data['guest']['lastname'])) {
			$data['lastname'] = $this->session->data['guest']['lastname'];
		} else {
			$data['lastname'] = '';
		}

		if (isset($this->session->data['guest']['email'])) {
			$data['email'] = $this->session->data['guest']['email'];
		} else {
			$data['email'] = '';
		}

		if (isset($this->session->data['guest']['telephone'])) {
			$data['telephone'] = $this->session->data['guest']['telephone'];
		} else {
			$data['telephone'] = '';
		}

		if (isset($this->session->data['guest']['fax'])) {
			$data['fax'] = $this->session->data['guest']['fax'];
		} else {
			$data['fax'] = '';
		}

		if (isset($this->session->data['payment_address']['company'])) {
			$data['company'] = $this->session->data['payment_address']['company'];
		} else {
			$data['company'] = '';
		}

		if (isset($this->session->data['payment_address']['address_1'])) {
			$data['address_1'] = $this->session->data['payment_address']['address_1'];
		} else {
			$data['address_1'] = '';
		}

		if (isset($this->session->data['payment_address']['address_2'])) {
			$data['address_2'] = $this->session->data['payment_address']['address_2'];
		} else {
			$data['address_2'] = '';
		}

		if (isset($this->session->data['payment_address']['postcode'])) {
			$data['postcode'] = $this->session->data['payment_address']['postcode'];
		} elseif (isset($this->session->data['shipping_address']['postcode'])) {
			$data['postcode'] = $this->session->data['shipping_address']['postcode'];
		} else {
			$data['postcode'] = '';
		}

		if (isset($this->session->data['payment_address']['city'])) {
			$data['city'] = $this->session->data['payment_address']['city'];
		} else {
			$data['city'] = '';
		}

		if (isset($this->session->data['payment_address']['country_id'])) {
			$data['country_id'] = $this->session->data['payment_address']['country_id'];
		} elseif (isset($this->session->data['shipping_address']['country_id'])) {
			$data['country_id'] = $this->session->data['shipping_address']['country_id'];
		} else {
			$data['country_id'] = $this->config->get('config_country_id');
		}

		if (isset($this->session->data['payment_address']['zone_id'])) {
			$data['zone_id'] = $this->session->data['payment_address']['zone_id'];
		} elseif (isset($this->session->data['shipping_address']['zone_id'])) {
			$data['zone_id'] = $this->session->data['shipping_address']['zone_id'];
		} else {
			$data['zone_id'] = '';
		}

		$this->load->model('localisation/country');

		$data['countries'] = $this->model_localisation_country->getCountries();

		// Custom Fields
		$this->load->model('account/custom_field');

		$data['custom_fields'] = $this->model_account_custom_field->getCustomFields();

		if (isset($this->session->data['guest']['custom_field'])) {
			if (isset($this->session->data['guest']['custom_field'])) {
				$guest_custom_field = $this->session->data['guest']['custom_field'];
			} else {
				$guest_custom_field = array();
			}

			if (isset($this->session->data['payment_address']['custom_field'])) {
				$address_custom_field = $this->session->data['payment_address']['custom_field'];
			} else {
				$address_custom_field = array();
			}

			$data['guest_custom_field'] = $guest_custom_field + $address_custom_field;
		} else {
			$data['guest_custom_field'] = array();
		}

		$data['shipping_required'] = $this->cart->hasShipping();

		if (isset($this->session->data['guest']['shipping_address'])) {
			$data['shipping_address'] = $this->session->data['guest']['shipping_address'];
		} else {
			$data['shipping_address'] = true;
		}

		// Captcha
		if ($this->config->get($this->config->get('config_captcha') . '_status') && in_array('guest', (array)$this->config->get('config_captcha_page'))) {
			$data['captcha'] = $this->load->controller('extension/captcha/' . $this->config->get('config_captcha'));
		} else {
			$data['captcha'] = '';
		}

		$this->response->setOutput($this->load->view('checkout/guest', $data));
	}

	public function save() {
		$this->load->language('checkout/checkout');

		$json = array();

		// Validate if customer is logged in.
		if ($this->customer->isLogged()) {
			$json['redirect'] = $this->url->link('checkout/checkout', '', true);
		}

		// Validate cart has products and has stock.
		if ((!$this->cart->hasProducts() && empty($this->session->data['vouchers'])) || (!$this->cart->hasStock() && !$this->config->get('config_stock_checkout'))) {
			$json['redirect'] = $this->url->link('checkout/cart');
		}