This is a very simple tutorial for whmcs on how you can hide some fields in the whmcs ticket when the user creates a ticket in this example I am going to show you how you can hide whmcs ticket message
<div hidden class="form-group">
<label for="inputMessage">{$LANG.contactmessage}</label>
<textarea name="message" id="inputMessage" rows="12" class="form-control markdown-editor" data-auto-save-name="client_ticket_open">{""}</textarea>
</div>