newsupernova/vendor/magento/module-gift-message/etc/extension_attributes.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Api/etc/extension_attributes.xsd">
    <extension_attributes for="Magento\Sales\Api\Data\OrderInterface">
        <attribute code="gift_message" type="Magento\GiftMessage\Api\Data\MessageInterface" />
    </extension_attributes>
    <extension_attributes for="Magento\Sales\Api\Data\OrderItemInterface">
        <attribute code="gift_message" type="Magento\GiftMessage\Api\Data\MessageInterface" />
    </extension_attributes>
    <extension_attributes for="Magento\GiftMessage\Api\Data\MessageInterface">
        <attribute code="entity_id" type="string" />
        <attribute code="entity_type" type="string" />
    </extension_attributes>
    <extension_attributes for="Magento\Quote\Api\Data\TotalsAdditionalDataInterface">
        <attribute code="gift_messages" type="Magento\GiftMessage\Api\Data\MessageInterface[]" />
    </extension_attributes>
</config>