Facebook will not be forwarding individual SKAdNetwork Postbacks to MMPs. However, aggregate SKAN data will be passed back via Facebook’s Ads Insights API. See What is the difference between networks forwarding individual SKAN postbacks to Branch, rather than providing data via an API? Is one option better? and Is Facebook planning to share SKAN conversion values with MMPs? for more details.
Facebook has recently provided a spec to MMPs (including Branch) for pulling this data, and more details about that integration can be found in our FAQ here: https://help.branch.io/faq/docs/how-do-we-set-up-the-facebook-skan-integration-with-branch