You must check this box before you can upload a file.
Go ahead, check it.
Place an HTML block above the Simple file List shortcode. This is simply a checkbox followed by your message. You can add a link to the full text if you want.
<p> <input id="myCheckToUpoad" type="checkbox" name="Checkbox" value="YES">Check this Box. </p>
The key to the code above is the
Locate your current theme’s functions.php file.
Add this code, then save.
There are many improvements that could be made to this example, but this is basically all you need to get started.