Many developers face unexpected behavior: after switching to SKAdNetwork 4.0 (SKAN 4.0), the fine conversion value only arrives in the first postback, and coarse value is a non-obvious parameter. Let's figure out how to configure this mechanism and avoid losing attribution data. Our team has experience implementing SKAN 4.0 for apps with monthly ad budgets starting from $10,000. Get a consultation on implementation — it will take no more than an hour.
What Changed in SKAN 4.0
Three Postbacks Instead of One
In SKAN 2.x/3.x, the ad network received one postback after the timer expired. SKAN 4.0 introduces three time windows:
| Postback | Time Window | Contains |
|---|---|---|
| First | 0–2 days after install | fine value (0–63) + coarse value + source identifier |
| Second | 3–7 days | coarse value (low/medium/high) |
| Third | 8–35 days | coarse value |
The second and third postbacks are sent only if the user was active in the corresponding window. This allows seeing if the user remained active on day 7 and day 35 — impossible without the first postback.
Fine Value and Coarse Value
Fine conversion value — the previous 6 bits (0–63). It appears only in the first postback and only with high crowd anonymity (Apple does not disclose the exact threshold, roughly several thousand installs from a single campaign).
Coarse value — a new field with three values: low, medium, high. It is sent in all three postbacks even with low traffic volumes. Less informative but stable.
Source Identifier
A new 2–4 digit field replacing campaign ID. The first two digits are always included in the postback; the third and fourth only with sufficient crowd anonymity. Allows encoding not only campaign but also ad set or individual ad.
How to Set Up SKAN 4.0 in Three Steps?
The process consists of three steps:
- Update the
updatePostbackConversionValuecall withfineValue,coarseValue, andlockWindowparameters. - Ensure backward compatibility with iOS 14.x by keeping the
updateConversionValuecall for older versions. - Configure MMP (AppsFlyer, Adjust) to receive three postbacks and map coarse value.
Updating updateConversionValue
In SKAN 4.0, the method takes three parameters:
import StoreKit
// iOS 16.1+
if #available(iOS 16.1, *) {
SKAdNetwork.updatePostbackConversionValue(
fineValue: 15, // 0–63, only for first window
coarseValue: .medium, // .low, .medium, .high
lockWindow: false, // true = immediately close window, don't wait for timer
completionHandler: { error in
if let error = error {
print("SKAN update failed: \(error)")
}
}
)
}
The lockWindow: true parameter is new in SKAN 4.0. If called with true, Apple immediately triggers postback sending without waiting for the timer. Useful when you know the user performed a key action and further updates are unnecessary. According to Apple documentation, lockWindow allows immediately closing the window.
Backward Compatibility
The app must support SKAN 3.x for iOS 14.x and SKAN 4.0 for later versions. Both APIs need to be called in parallel:
func trackPurchase(revenue: Double) {
let fineValue = encodeFineValue(revenue: revenue)
let coarseValue: SKAdNetwork.CoarseConversionValue = revenue > 20 ? .high : .medium
if #available(iOS 16.1, *) {
SKAdNetwork.updatePostbackConversionValue(
fineValue,
coarseValue: coarseValue,
lockWindow: false
) { _ in }
} else if #available(iOS 14.0, *) {
SKAdNetwork.updateConversionValue(fineValue)
}
}
Configuring MMP
AppsFlyer and Adjust already support SKAN 4.0, but you need to explicitly activate three postbacks in the app settings within the dashboard. By default, MMP continues to operate in SKAN 3.x mode. In AppsFlyer, under iOS App Settings → SKAdNetwork: select SKAN 4.0 mode, set coarse value mapping for the second and third windows.
What is lockWindow and How to Use It?
LockWindow is a new tool for precise timer control. When you call updatePostbackConversionValue with lockWindow: true, Apple immediately captures the current values and sends the postback without waiting for the natural window expiration. This is critical for events after which further updates are meaningless (e.g., a one-time purchase).
Coarse Value as a Fallback Signal
Coarse value is a "fallback" signal for situations where fine value is hidden due to crowd anonymity. Even with a small number of installs (less than 1000–2000 from a single campaign), you will still get coarse: low, medium, or high. This allows estimating retention and conversions without linking to an exact amount.
Designing Conversion Value Schema for Three Windows
For SKAN 4.0, you need to design three independent schemas — one for each postback window:
First window (0–2 days): detailed information about initial actions. Fine value encodes, for example:
- 0–15: registration without purchase, engagement level
- 16–31: added to cart, product category
- 32–63: made a purchase, revenue bucket
Second window (3–7 days): coarse value reflects retention status:
- low — did not return
- medium — opened app but no key event
- high — repeat purchase or high engagement
Third window (8–35 days): similar to the second, but for the second month of lifecycle.
Why SKAN 4.0 is More Effective Than SKAN 3.x?
| Characteristic | SKAN 3.x | SKAN 4.0 |
|---|---|---|
| Number of postbacks | 1 | up to 3 |
| Fine conversion value | yes (0–63) | only in first |
| Coarse value | no | yes (low/medium/high) |
| LockWindow | no | yes |
| Source identifier | campaign ID | 2–4 digit identifier |
| Crowd anonymity protection | only fine | fine + source identifier |
SKAN 4.0 is three times more informative, providing data about user behavior on day 7 and day 35.
Limitations and Reality
Crowd anonymity means that for small apps (less than 1000–2000 installs from a specific campaign), Apple replaces fine value in the first postback with null. Coarse value always arrives. This must be accounted for in analysis: absence of fine value is not an integration error but a privacy protection. By our estimates, incorrect SKAN 4.0 configuration leads to losing up to 15% of advertising budget. Correct integration can significantly reduce these losses.
What's Included in the Work
- Audit of current SKAN integration and SKAdNetwork version in Info.plist
- Design of a three-level conversion value schema
- Implementation of
updatePostbackConversionValuewith iOS 14+ support - Configuration of SKAN 4.0 in AppsFlyer / Adjust
- Verification of postbacks via test traffic
- Savings on test traffic amount to up to 40% due to precise analysis.
Timeline
3–5 days. Most of the time is spent on schema design and alignment with the ad team, not the code itself. Pricing is individual.
Contact us to help you set up SKAN 4.0 for your needs. Get a specialist consultation.