RCP_Member::get_subscription_key PHP Method

    public function get_subscription_key()
    {
        $subscription_key = get_user_meta($this->ID, 'rcp_subscription_key', true);
        return apply_filters('rcp_member_get_subscription_key', $subscription_key, $this->ID, $this);
    }

 /**
  * Get the data being exported
  *
  * @access      public
  * @since       1.5
  * @return      array
  */
 public function get_data()
 {
     global $wpdb;
     $data = array();
     $subscription = isset($_POST['rcp-subscription']) ? absint($_POST['rcp-subscription']) : null;
     $status = isset($_POST['rcp-status']) ? sanitize_text_field($_POST['rcp-status']) : 'active';
     $offset = isset($_POST['rcp-offset']) ? absint($_POST['rcp-offset']) : null;
     $number = isset($_POST['rcp-number']) ? absint($_POST['rcp-number']) : null;
     $members = rcp_get_members($status, $subscription, $offset, $number);
     if ($members) {
         foreach ($members as $member) {
             $member = new RCP_Member($member->ID);
             $discounts = get_user_meta($member->ID, 'rcp_user_discounts', true);
             if (!empty($discounts) && is_array($discounts) && !$discounts instanceof stdClass) {
                 foreach ($discounts as $key => $code) {
                     if (!is_string($code)) {
                         unset($discounts[$key]);
                     }
                 }
                 $discounts = implode(' ', $discounts);
             }
             $data[] = array('user_id' => $member->ID, 'user_login' => $member->user_login, 'user_email' => $member->user_email, 'first_name' => $member->first_name, 'last_name' => $member->last_name, 'subscription' => $member->get_subscription_id(), 'subscription_key' => $member->get_subscription_key(), 'expiration' => $member->get_expiration_date(), 'status' => $member->get_status(), 'discount_codes' => $discounts, 'profile_id' => $member->get_payment_profile_id(), 'is_recurring' => $member->is_recurring());
         }
     }
     $data = apply_filters('rcp_export_get_data', $data);
     $data = apply_filters('rcp_export_get_data_' . $this->export_type, $data);
     return $data;
 }