Magento – Magento 2 Configuration Issue for custome module

a:4:{i:0;s:134:"Notice: Undefined index: id in
C:\xampp\htdocs\sea\vendor\magento\module-config\Model\Config\Structure\Element\Iterator.php
on line 59";i:1;s:6225:"#0
C:\xampp\htdocs\sea\vendor\magento\module-config\Model\Config\Structure\Element\Iterator.php(59):
Magento\Framework\App\ErrorHandler->handler(8, 'Undefined index…',
'C:\xampp\htdocs…', 59, Array)

This is my system.xml file

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Backend/etc/system_file.xsd">
    <system>
        <section id="iwd_opc" translate="label" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>One Step Checkout</label>
            <tab>iwd</tab>
            <resource>IWD_Opc::system_config</resource>

            <group id="info" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>Info</label>
                <field id="version" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>Version</label>
                    <frontend_model>IWD\Opc\Block\Adminhtml\System\Config\Version</frontend_model>
                </field>
                <field id="documentation" translate="label" type="text" sortOrder="2" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>Documentation</label>
                    <frontend_model>IWD\Opc\Block\Adminhtml\System\Config\Documentation</frontend_model>
                </field>
            </group>

            <group id="general" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>General Settings</label>
                <field id="enable_in_frontend" translate="label" type="select" sortOrder="5" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Enable</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
                <field id="opc_title" translate="label" type="text" sortOrder="6" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Meta Title</label>
                </field>

                <field id="opc_discount_enable" translate="label" type="select" sortOrder="7" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Display Discount Field</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>

                <field id="onepage_checkout_comments_enabled" translate="label" type="select" sortOrder="99" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Enable Order Comments?</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
            </group>

        </section>
    </system>
</config>

this is acl.xml

<?xml version="1.0"?>

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Acl/etc/acl.xsd">
    <acl>
        <resources>
            <resource id="Magento_Backend::admin">
                <resource id="Magento_Backend::stores">
                    <resource id="Magento_Backend::stores_settings">
                        <resource id="Magento_Config::config">
                            <resource id="IWD_StoreCredit::system_config" title="IWD Store Credit" />
                        </resource>
                    </resource>
                </resource>
            </resource>
        </resources>
    </acl>
</config>