Error code

I am getting below error. Can you help me understand what might have caused this error ?

[Sun Oct 14 00:44:30.744351 2018] [:error] [pid 17894] [client 50.47.138.174:23313] billing_email was called incorrectly. Order properties should not be accessed directly. Backtrace: require(‘wp-blog-header.php’), require_once(‘wp-includes/template-loader.php’), do_action(‘template_redirect’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_AJAX::do_wc_ajax, do_action(‘wc_ajax_checkout’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_AJAX::checkout, WC_Checkout->process_checkout, WC_Checkout->process_order_payment, WC_Gateway_PayPal_Pro_PayFlow_AngellEYE->process_payment, WC_Gateway_PayPal_Pro_PayFlow_AngellEYE->do_payment, WC_Order->update_status, WC_Order->save, WC_Order->status_transition, do_action(‘woocommerce_order_status_pending_to_failed’), WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Emails::send_transactional_email, do_action_ref_array, WP_Hook->do_action, WP_Hook->apply_filters, call_user_func_array, WC_Email_Failed_Order->trigger, WC_Email->get_recipient, apply_filters(‘woocommerce_email_recipient_failed_order’), WP_Hook->apply_filters, call_user_func_array, wc_cancelled_order_add_customer_email, WC_Abstract_Legacy_Order->__get, wc_doing_it_wrong. This message was added in version 3.0., referer: https://www.wyzecam.com/checkout/