According to https://www.revenuecat.com/docs/integrations/attribution/facebook-ads:
The Facebook integration requires some device-specific data. RevenueCat will only send events into Facebook Ads Manager if the below Attribute keys have been set for the device.
$idfa | iOS advertising identifier UUID | Required:  (iOS only) |
95% of users opt out of app tracking, so the IDFA won’t be available. Does this mean Meta won’t see conversions 95% of the time? Is it possible to send conversion events with just, say, IP, email, and phone numbers?
