The traffic came from a domain that by Safari is classified as having third-party tracking capabilities.
The final URL (to your website) includes a query or fragment identified (e.g. a click ID).
A user clicks one of your ads on Facebook and is sent to:
Once the user lands on your website, Facebook will create a cookie that is linked with this click ID so that subsequent conversions can be attributed to the correct ad click. However, with ITP 2.2 this conversion will need to happen during the same day, as the cookie will be deleted after 1 day.
Webkit, the search engine used by Safari, recently published it’s Tracking Prevention Policy (see here: https://webkit.org/tracking-prevention-policy/). The policy outlines a number of intended and un-unintended impacts by ITP 2.1 and 2.2.