To setup ProveSource auto tracking feature with SendinBlue lead forms,
you must embed the SendinBlue form using one of two options:
HTML Embed Code to copy to your site
Simple HTML embed code to copy on your site
The iframe option will not work - there is no option to embed ProveSource code in it.
After embedding using option #1 or #2, make sure ProveSource is installed in the same page you're embedding the form in.