SKAdNetwork

Definition

SKAdNetwork is Apple's StoreKit framework that attributes app installs to advertising campaigns without exposing a device identifier, by having the operating system send a delayed, aggregated postback to the ad network that won the install.

It exists because attribution used to work by matching an IDFA on the ad click to the same IDFA on the install, and ATT removed that identifier for most users. SKAdNetwork replaces the join: the device does the matching internally and reports the outcome with the identifiers stripped, the timing randomised, and the payload deliberately small. Everything that makes SKAN awkward to work with is a consequence of that trade.

The version history, and why it matters to your schema

SKAN's capabilities changed substantially across versions, and a schema designed for 2.x throws away most of what 4.0 can carry.

4.0 is the version to design for, and its headline change is that a campaign no longer gets one shot at a single number. Three conversion windows mean you can measure an install, then a day-7 signal, then a day-35 signal, from the same ad.

The source identifier and the anonymity tiers

4.0 replaced the flat 0–99 campaign ID with a hierarchical source-identifier of two, three or four digits. You always get the first two. Whether the remaining digits and the conversion value survive depends on the install cohort's crowd anonymity tier — Apple's measure of whether a cohort is large enough that a report cannot single out a person.

Read the hierarchy outwards from the two digits you always receive: put your most important dimension there — campaign, or geo — and the finer splits in digits three and four, because those are the ones a low-volume campaign loses. A network that encodes campaign in digit four gets no campaign reporting at all on small campaigns.

Registering, and what the postback looks like

An advertised app declares every ad network permitted to claim its installs. A network absent from this list receives nothing, which is the first thing to check when a partner reports zero SKAN volume.

<key>SKAdNetworkItems</key>
<array>
  <dict>
    <key>SKAdNetworkIdentifier</key>
    <string>example123.skadnetwork</string>
  </dict>
  <dict>
    <key>SKAdNetworkIdentifier</key>
    <string>partner456.skadnetwork</string>
  </dict>
</array>

<!-- Get your own copy of winning postbacks -->
<key>NSAdvertisingAttributionReportEndpoint</key>
<string>https://postbacks.example.com</string>

{
  "version": "4.0",
  "ad-network-id": "example123.skadnetwork",
  "source-identifier": "5239",
  "app-id": 525463029,
  "transaction-id": "6aafb7a5-0170-41b5-bbe4-fe71dedf1e28",
  "redownload": false,
  "source-domain": "example.com",
  "fidelity-type": 1,
  "did-win": true,
  "postback-sequence-index": 0,
  "conversion-value": 20,
  "coarse-conversion-value": "high",
  "attribution-signature": "MEQCIQD..."
}

• fidelity-type is 1 for a StoreKit-rendered click and 0 for a view-through impression. Mixing them in one report inflates your click performance.
• postback-sequence-index is 0, 1 or 2 and tells you which window this is. Without it, three postbacks for one install look like three installs.
• did-win is false for networks that were in the running and lost — count only wins.
• source-domain appears for web-to-app; source-app-id for app-to-app. Neither is guaranteed.
• attribution-signature must be verified against Apple's public key, or your endpoint will accept fabricated installs.

Where SKAdNetwork stands now

AdAttributionKit is SKAN's successor and has been available since iOS 17.4. Apple has not published a SKAdNetwork deprecation date, and SKAN is still where the overwhelming majority of iOS attribution volume lands, so the honest position is that SKAN is the present and AdAttributionKit is the direction.

The practical consequence is that you maintain one conversion value schema and feed it to both frameworks, rather than treating them as a migration. The bit budget, the windows and the anonymity tiers are shared, so a schema designed properly for SKAN 4.0 is already an AdAttributionKit schema.