Its being created under
System->Config->General->Customers:
<code>
<config>
<system>
<section id="trade_customer" translate="label" type="text" sortOrder="100" showInDefault="1" showInWebsite="1" showInStore="1">
<class>separator-top</class>
<label>Trade Customer</label>
<tab>customer</tab>
<resource>Magento_Customer::config_general</resource>
<group id="general" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
<label>General Configuration</label>
<field id="error_used_message" translate="label" type="text" sortOrder="4" showInDefault="1" showInWebsite="1" showInStore="1">
<label>Error ID Used Response Message</label>
<comment>The error message will display when certificate ID has been previously used</comment>
</field>
</group>
</section>
</system>
</config>
</code>