magento-test/app/code/Magento/Payment/Test/Mftf/ActionGroup/ApplyCouponOnPaymentPageActionGroup.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
 /**
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
-->

<actionGroups xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:noNamespaceSchemaLocation="urn:magento:mftf:Test/etc/actionGroupSchema.xsd">
    <actionGroup name="ApplyCouponOnPaymentPageActionGroup">
        <annotations>
            <description>Adds the provided Coupon Code on the Storefront Shopping Cart page. Validates that the Discount Verification Message is present and correct.</description>
        </annotations>
        <arguments>
            <argument name="couponCode" type="string"/>
        </arguments>

        <click selector="{{ProductCardSection.addCoupon}}" stepKey="clickToAddDiscount"/>
        <fillField selector="{{ProductCardSection.addCode}}" userInput="{{couponCode}}" stepKey="TypeDiscountCode"/>
        <click selector="{{ProductCardSection.applyDiscount}}" stepKey="clickToApplyDiscount"/>
        <waitForPageLoad stepKey="WaitForDiscountToBeAdded"/>
        <!-- Success message will change to display none so will check DOM instead -->
        <seeElementInDOM selector="{{ProductCardSection.discountSuccessMsgInDOM}}" stepKey="discountApplyMessage"/>
    </actionGroup>
</actionGroups>