You can use Zapier to connect StealthSeminar with Facebook Conversion API. Zapier charges you for each visitor as well as each event (or task).
Example: If you have 200 visitors to a webinar and are tracking:
Attending the first half of your webinar
Attending your webinar to the call to action appearing
That would be 200 attendees x 4 tasks = 800 tasks (Zapiers terms for connections). That will cost you $19.99 USD (at this time of KB article update).
That is for a single instance of the webinar so times that by the number of webinars, attendees, and tasks you have.
With the StealthSeminar Capi Plugin, the fee is just $19.95 a month for unlimited attendees and tasks.
You can send any event using the connection to CAPI i.e Facebook Conversion API, e.g. Lead event when someone registers for the webinar.
If you have any questions feel free to chat with support!