magento-test/app/code/Magento/GiftMessage/etc/webapi.xml

<?xml version="1.0"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<routes xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Webapi:etc/webapi.xsd">
    <!-- For authorized customer -->
    <route url="/V1/carts/:cartId/gift-message" method="GET">
        <service class="Magento\GiftMessage\Api\CartRepositoryInterface" method="get"/>
        <resources>
            <resource ref="Magento_Sales::create" />
        </resources>
    </route>
    <route url="/V1/carts/:cartId/gift-message/:itemId" method="GET">
        <service class="Magento\GiftMessage\Api\ItemRepositoryInterface" method="get"/>
        <resources>
            <resource ref="Magento_Sales::create" />
        </resources>
    </route>
    <route url="/V1/carts/:cartId/gift-message" method="POST">
        <service class="Magento\GiftMessage\Api\CartRepositoryInterface" method="save"/>
        <resources>
            <resource ref="Magento_Sales::create" />
        </resources>
    </route>
    <route url="/V1/carts/:cartId/gift-message/:itemId" method="POST">
        <service class="Magento\GiftMessage\Api\ItemRepositoryInterface" method="save"/>
        <resources>
            <resource ref="Magento_Sales::create" />
        </resources>
    </route>

    <!-- For current customer -->
    <route url="/V1/carts/mine/gift-message" method="GET">
        <service class="Magento\GiftMessage\Api\CartRepositoryInterface" method="get"/>
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="cartId" force="true">%cart_id%</parameter>
        </data>
    </route>
    <route url="/V1/carts/mine/gift-message/:itemId" method="GET">
        <service class="Magento\GiftMessage\Api\ItemRepositoryInterface" method="get"/>
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="cartId" force="true">%cart_id%</parameter>
        </data>
    </route>
    <route url="/V1/carts/mine/gift-message" method="POST">
        <service class="Magento\GiftMessage\Api\CartRepositoryInterface" method="save"/>
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="cartId" force="true">%cart_id%</parameter>
        </data>
    </route>
    <route url="/V1/carts/mine/gift-message/:itemId" method="POST">
        <service class="Magento\GiftMessage\Api\ItemRepositoryInterface" method="save"/>
        <resources>
            <resource ref="self" />
        </resources>
        <data>
            <parameter name="cartId" force="true">%cart_id%</parameter>
        </data>
    </route>

    <!-- For guests -->
    <route url="/V1/guest-carts/:cartId/gift-message" method="GET">
        <service class="Magento\GiftMessage\Api\GuestCartRepositoryInterface" method="get"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V1/guest-carts/:cartId/gift-message/:itemId" method="GET">
        <service class="Magento\GiftMessage\Api\GuestItemRepositoryInterface" method="get"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V1/guest-carts/:cartId/gift-message" method="POST">
        <service class="Magento\GiftMessage\Api\GuestCartRepositoryInterface" method="save"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
    <route url="/V1/guest-carts/:cartId/gift-message/:itemId" method="POST">
        <service class="Magento\GiftMessage\Api\GuestItemRepositoryInterface" method="save"/>
        <resources>
            <resource ref="anonymous" />
        </resources>
    </route>
</routes>