What are the SKAdNetwork privacy thresholds?

A postback from SKAdNetwork 2.2 (available in iOS 14.5) will look like this:

{
  "version" : "2.2",
  "ad-network-id" : "com.example",
  "campaign-id" : 42,
  "transaction-id" : "6aafb7a5-0170-41b5-bbe4-fe71dedf1e28",
  "app-id" : 525463029,
  "attribution-signature" : "MEYCIQDTuQ1Z4Tpy9D3aEKbxLl5J5iKiTumcqZikuY/AOD2U7QIhAJAaiAv89AoquHXJffcieEQXdWHpcV8ZgbKN0EwV9/sY",
  "redownload": true,
  "source-app-id": 1234567891,
  "fidelity-type": 1,
  "conversion-value": 20
}

See this Apple documentation page for more details.

Of these parameters, conversion-value and source-app-id will only be included when they meet a secret Apple 'privacy threshold'. This is in order to protect user privacy. Apple has not released any details about what this threshold is, and many ad networks are currently (as of February, 2021) reporting that very few postbacks include them.

In Branch's own reporting, activity that hasn't met the minimum privacy threshold will show these values as "Unpopulated"; activity that has met this threshold will include the appropriate value.