Passing Parameters to Popups/Sticky Bars


Apologies if I am in the wrong place - complete newbie to Unbounce…

I have a Wordpress page with a series of buttons on.
On selecting any of the buttons, an Unbounce Popup should appear for the user to complete their details and submit the LEAD to Unbounce.

This is all working great - so I have the Popup created and am using the Embed link in the WP form, and when any button is selected (with the correct element = “When a visitor clicks an element with…”) the form pops up.

My question is this:
I want to know WHICH button on the WP form the user selected - so that I can pass this info to Unbounce in a hidden field/parameter and then send on to our Lead recording API back at base…

As the only script that is pasted in is the EMBED URL, how can I do this?

Your help is appreciated.