The problem is just in webform, because Zoho Documentation says "add the following line code into you webform"

"<input type='hidden' id="zc_gad" name="zc_gad" value=""/>"

Ok, this is the problem. I cant add a custom line into webform, but I can add a custom element in webform with "name" and "value" fields hidden (screenshot)

There is any error? What is the correct way to setup it?