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:
Successful registrations
Webinar attendance
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.
https://zapier.com/apps/stealthseminar/integrations/facebook-conversions
If you have any questions feel free to chat with support!