SyntaxError in WordPress plugin

First of all, sorry for lame question. I have spent few days trying to find solution to my problem but my knowledge of PHP is just poor.

I have a WordPress plugin that is made to integrate Armenian bank system with WooCommerce. On the front, when checking this method of payment and clicking Next, it gives Internal server error. After debugging it gives: SyntaxError: Unexpected token a in JSON at position 0.

Can anyone take a look on the code and tell me like to an idiot what to do? Thanks in advance.

<?php

class WC_ArCa extends WC_Payment_Gateway

{

private $environment;

private $username;

private $password;

/**

 * WC_ArCa constructor.

 */

function __construct()

{

    $this->id = "arca";

    // The Title shown on the top of the Payment Gateways Page next to all the other Payment Gateways

    $this->method_title = __("ArCa", 'ArCa');

    // The description for this Payment Gateway, shown on the actual Payment options page on the backend

    $this->method_description = __("Description", 'ArCa payment gateway');

    // The title to be used for the vertical tabs that can be ordered top to bottom

    $this->title = __("Title", 'ArCa');

    // If you want to show an image next to the gateway's name on the frontend, enter a URL to an image.

    $this->icon = null;

    // Bool. Can be set to true if you want payment fields to show on the checkout

    // if doing a direct integration, which we are doing in this case

    $this->has_fields = true;

    // This basically defines your settings which are then loaded with init_settings()

    $this->init_form_fields();

    // After init_settings() is called, you can get the settings and load them into variables, e.g:

    // $this->title = $this->get_option( 'title' );

    $this->init_settings();

    // True if test mode is enabled

    $this->environment = $this->settings['environment'];

    // ArCa username

    $this->username = $this->settings['username'];

    // ArCa password

    $this->password = $this->settings['password'];

    // Lets check for SSL

    //add_action('admin_notices', array($this, 'do_ssl_check'));

    // Save settings

    if (is_admin()) {

        // Versions over 2.0

        // Save our administration options. Since we are not going to be doing anything special

        // we have not defined 'process_admin_options' in this class so the method in the parent

        // class will be used instead

        add_action('woocommerce_update_options_payment_gateways_' . $this->id, array(

            $this,

            'process_admin_options'

        ));

    }

}

// Build the administration fields for this specific Gateway

public function init_form_fields()

{

    $this->form_fields = array(

        'enabled' => array(

            'title' => __('Enable / Disable', 'arca'),

            'label' => __('Enable this payment gateway', 'arca'),

            'type' => 'checkbox',

            'default' => 'yes',

        ),

        'title' => array(

            'title' => __('Title', 'arca'),

            'type' => 'text',

            'desc_tip' => __('Payment title the customer will see during the checkout process.', 'arca'),

            'default' => __('card', 'arca'),

        ),

        'description' => array(

            'title' => __('Description', 'arca'),

            'type' => 'textarea',

            'desc_tip' => __('Payment description the customer will see during the checkout process.', 'arca'),

            'default' => __('Pay securely using your credit card.', 'arca'),

            'css' => 'max-width:350px;'

        ),

        'username' => array(

            'title' => __('Username', 'username'),

            'type' => 'text',

            'desc_tip' => __('Username description.', 'username'),

        ),

        'password' => array(

            'title' => __('Password', 'password'),

            'type' => 'password',

            'desc_tip' => __('Password description.', 'password'),

        ),

        'environment' => array(

            'title' => __('ArCa Test Mode', 'arca'),

            'label' => __('Enable Test Mode', 'arca'),

            'type' => 'checkbox',

            'description' => __('Place the payment gateway in test mode.', 'arca'),

            'default' => 'yes',

        )

    );

}

/**

 * Submit payment and handle response

 *

 * @param int $order_id

 * @throws Exception

 *

 * @return mixed

 */

public function process_payment($order_id)

{

    // Get this Order's information so that we know

    // who to charge and how much

    $customer_order = new wc_get_order( $order_id );

    // Are we testing right now or is it a real transaction

    $environment = ($this->environment == "yes") ? 'TRUE' : 'FALSE';

    // Decide which URL to post to

    $environment_url = ("FALSE" == $environment)

        ? 'https://ipay.arca.am/payment/rest/'

        : 'https://ipaytest.arca.am:8444/payment/rest';

    // This is where the fun stuff begins

    $payload = array(

        "userName" => $this->username,

        "password" => $this->password,

        "amount" => intval($customer_order->get_total) * 100,

        "returnUrl" => $this->get_return_url($customer_order),

        "orderNumber" => intval($customer_order->get_order_number()) + 119332,

    );

    // Send this payload to Authorize.net for processing

    $response = wp_remote_post($environment_url . "registerPreAuth.do", array(

        'method' => 'POST',

        'body' => http_build_query($payload),

        'timeout' => 90,

        'sslverify' => false,

    ));

    if (is_wp_error($response)) {

       throw new Exception(__('We are currently experiencing problems trying to connect to this payment gateway. Sorry for the inconvenience.', 'arca'));

    }

    if (empty($response['body'])) {

        throw new Exception(__('ArCa\'s Response was empty.', 'arca'));

    }

    // Retrieve the body's response if no errors found

    $response_body = wp_remote_retrieve_body($response);

    if (isset($response_data["errorCode"]) && isset($response_data["formUrl"])) {

        if ($response_data["errorCode"] == 0) {

            return array(

                'result' => 'success',

                'redirect' => $response_data['formUrl'],

            );

        } else {

            throw new Exception(__($response_data["errorMessage"], 'arca'));

        }

    }

    throw new Exception(__("Error processing checkout, please try again.", 'arca'));

}

}