<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
<default>
    <payment>
        <xpay>
            <active>0</active>
            <model>NexiXPayModelPaymentMethod</model>
            <title>Credit Card</title>
            ...
        </xpay>
        <xpay_cc_vault>
            <model>XPayCreditCardVaultFacade</model>
            <title>Stored Cards (XPay)</title>
        </xpay_cc_vault>
    </payment>
</default>

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <section id="payment">

            <group id="xpay" translate="label" type="text" sortOrder="325148" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>Nexi XPay</label>
                <field id="active" translate="label" type="select" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="0">
                    <label>Enabled</label>
                    <source_model>MagentoConfigModelConfigSourceYesno</source_model>
                    <config_path>payment/xpay/active</config_path>
                    <comment><![CDATA[Enable Nexi Payment Module.]]></comment>
                </field>