Hello everyone!
We are currently trying to implement Conversions API on Facebook. As we know, HubSpot has this integration as a beta, so we are doing this integration manually.
One of the requirements is to have a leadgen_id (unique identifier for facebook conversions). This property should show up in HubSpot, but we can’t find it.
Has anyone done this integration manually? How did you manage to implement it?
Regards,
@hhawk ,
Curious if you could help out here a bit 
Dear @lucascarabajal
You may try using the HubSpot Contact ID… Below is a more complete answer. I hope this helps. You should also consider trying to use Facebook’s Click ID (FBCLID), which is a URL parameter.
I’m testing the HS beta for CAPI but have overseen it’s implemention elsewhere previously (not using HubSpot). I may be able to offer some insight.
CAPI works in part because FB are able to de-dup data that is sent from both the browser and the server and there are a few ways that FB can do this. You need to send matching event data from both the pixel and the server.
This is explained here --> https://www.facebook.com/business/help/823677331451951?id=1205376682832142
You can use Facebook Click ID (FBCLID), FBP (an ID set by the FB Pixel as a cookie), or an ExternID (an external ID that doens’t contact PII (personal information).
Which evet set of data you send (see the FB link above) you need to send it from the pixel and the server.
If you are looking for the ExternID you could use the HubSpot ID (contact ID), but you would have to send it via the Pixel as well.