A Pay Per Lead offer is an offer where you get paid each time a user performs a defined action. For example, a PPL payout might mean you get paid anytime a user registers for free, fills out a form, or submits their e-mail. More specifically: SOI – single opt-in (the user simply submits his email address without confirming); DOI – double opt-in (the user submits his email address and confirms within the mail he got).