Hi Yuniar and AMurray,
Thanks for your help.
I have figured out how it work by using url parameter. I guess a better explanation is needed on the documentation page (placeholder code).
Here below is your team's reply on my ticket. Easier to follow.
"The easy way you can put a single line text field to hold the url on first page. (Create a text field in the form, and make it hidden)
Then define the url on get variable when you put the embed code on web page.
For example, if the single line text field id is 5, you can set like this :
<div id="mf_placeholder"
data-formurl="http://domain/machform/embed.php?id=12859&element_5=http://your_source_url"
data-formheight="1166"
data-paddingbottom="10">
</div>
PS. Yuniar, any plan to move machform into wordpress, perhaps a plugin for WP? I know it is a lot of work.