Google Adwords Integration

Google Adwords Integration

I'm trying to integrate Adwords with Zoho crm but the instructions appear to be missing important bits of information.

I am using my own forms and api.

I have captured the GCLID from cookie and assigned it to variable $gclid and have included this is the api i.e.
<FL val="GCLID">'.$gclid.'</FL>

So far so good. However, I'm confused as to what goes in the hidden field in the form.

Is it <input type='hidden' id="zc_gad" name="zc_gad" value=""/> ?
Or is it <input type='hidden' id="zc_gad" name="zc_gad" value="'.$gclid.'"/> ?

And is it even necessary to include the hidden field?

I have included <script type="text/javascript" src='https://crm.zoho.eu/crm/javascript/zcga.js'></script> before the </body> tag.