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Only one SKAN postback, never the second or third

Missing second and third SKAN postbacks usually trace to tier 0, SKAN 3 ads, legacy update calls or non-winning installs. Learn which applies and how to fix it.

Run the skan null values troubleshooter →
SymptomYou receive the first SKAN postback for installs, but never the second or third.
Most likely causeThe install falls into tier 0, the ad was signed with SKAN 3 or earlier, or the app uses the older update method.
First checkCheck the SKAN version of the postbacks and which update method your app or MMP SDK calls.

Short answer: SKAN 4 can send up to three postbacks for a winning install, but only on iOS 16.1 and later, with ads signed for SKAN 4, and not at crowd anonymity tier 0. The older update method also works only in the first window. Non-winning installs only ever get the first postback.

Why later SKAN postbacks go missing

Multiple conversion windows: SKAN 4 splits measurement into three windows, days 0 to 2, 3 to 7 and 8 to 35 after first launch, each able to produce one postback for the winning ad.

If any requirement for multiple postbacks is not met, Apple sends at most the first one.

Which condition is most likely?

Check the version field and tier first: SKAN 3 ads and tier 0 installs explain most cases. If both look fine, check which update method the app calls.

Likely causes

  • Tier 0. Apple says tier 0 gets no second or third postback.
  • SKAN 3 or earlier. Multiple postbacks need iOS 16.1 or later and ads signed with SKAN 4.
  • Legacy update method. Apple says the older updatePostbackConversionValue method without a coarse value works only in the first window and has no multiple postbacks.
  • Non-winning attribution. Non-winning postbacks are only sent for the first window.
  • Still waiting. The second and third postbacks arrive 24 to 144 hours after their windows close. See late SKAN postbacks.

How to confirm it

  1. Check the version field of the first postbacks you receive.
  2. Check the source identifier length: 2 digits with no value suggests tier 0.
  3. Search your code or MMP SDK for which update method is called after day 2.
  4. Exclude did-win false postbacks from the count.
  5. Allow at least 41 days after install before concluding that a third postback is missing, since the last window ends on day 35 and the delay can reach 144 hours.

How to fix it

  1. Call updatePostbackConversionValue with the coarseValue and lockWindow parameters.
  2. Set coarse values during days 3 to 7 and 8 to 35 for retention or revenue milestones.
  3. Ask your ad networks to sign ads with SKAN 4.
  4. Raise volume per campaign where possible to move out of tier 0 (general practice).
RequirementNeeded for postbacks 2 and 3
iOS version16.1 or later
Ad signatureSKAN 4
Update methodWith coarseValue and lockWindow
Crowd anonymityTier 1 or above
AttributionWinning

The SKAN null values troubleshooter includes these checks, and the SKAN 4 postbacks guide explains each window. For postbacks that arrive but are empty, see SKAN null conversion values.

Related

Related symptoms

iOS SKANSecond and third SKAN postbacks arrive days lateApple adds a random delay of 24 to 144 hours after the second and third windows close.→iOS SKANNo SKAN postbacks arriving at allThe app never registers the install with SKAN, or the postbacks are still inside Apple's random delay.→iOS SKANSKAN postbacks with a null conversion valueThe postback is non-winning, falls into a low crowd anonymity tier, or the app never set a value.→
FAQ

Common questions

How many SKAN postbacks can an install produce?

Up to three for the winning ad under SKAN 4, one per conversion window. Non-winning ads get only the first.

Do second and third postbacks carry fine values?

No. Apple ignores fine values after the first window, so later postbacks carry only a coarse value.

How long until the third postback arrives?

The third window ends on day 35 after first launch, then Apple adds 24 to 144 hours. Allow roughly six weeks from install.

Can I end a window early?

Yes. Setting lockWindow to true finalises the value for that window, and Apple then starts the postback delay.

What is mobile attribution?

Mobile attribution is the process of crediting each app install or in-app event to the ad, link or channel that drove it. A mobile measurement partner (MMP) does this across all your channels so each install is counted once.

Why do ad networks report more installs than my MMP?

Each network counts every install it touched within its own windows, including views, while an MMP gives each install to a single source. Adding the networks' numbers together therefore overstates real installs.