Facebook Lead Ads API doesn't create new person in Marketo

Hi community,
I've been working with the Facebook Lead Ads API for the past few days. I noticed that it only updates the activity log for people who already exist in Marketo. However, it doesn't create a new person when someone who isn't already in Marketo submits a lead form on Facebook.

I'm not sure why it's not working as expected. The API correctly updates the activity "Filled out Facebook Lead Form" in the activity log for people who already exist in the database, so it doesn't seem to be a field mapping issue. I also checked the "Person Source" field, and there's no value indicating "Facebook Lead Ads".

Has anyone else encountered this issue before? Any insights or suggestions would be greatly appreciated. Thank you in advance!