The tracking call is one line. Place it where your purchase observer sees a successful transaction — the same callback you'd already use to grant entitlement to the user. Avoid the temptation to pass price, currency, product SKU, or user ID; Respectlytics's API rejects extra fields with a 400 Bad Request, so this fails fast in development if a teammate adds a field by reflex.
▸ Install the Kotlin (Android) SDK
// build.gradle.kts (app module)
dependencies {
implementation("com.respectlytics:respectlytics-kotlin:3.0.0")
}Pure Kotlin coroutines implementation. No Java dependencies, no Google Play Services dependencies. ~300KB DEX overhead — compare to roughly 3.8MB for Firebase Analytics (a measurable cold-start improvement on lower-end devices).
▸ Initialize Respectlytics in Kotlin (Android)
import com.respectlytics.android.Respectlytics
class MyApplication : Application() {
override fun onCreate() {
super.onCreate()
Respectlytics.configure(this, appKey = "<YOUR_APP_KEY>")
}
}Initialize once in `Application.onCreate`. No additional permissions in the manifest — `INTERNET` is sufficient. The SDK does not request `AD_ID`, does not query `AdvertisingIdClient`, and does not declare `ACCESS_NETWORK_STATE`.
▸ Track the event in Kotlin (Android)
import com.android.billingclient.api.*
import com.respectlytics.android.Respectlytics
class PurchaseHandler : PurchasesUpdatedListener {
override fun onPurchasesUpdated(billingResult: BillingResult, purchases: List<Purchase>?) {
if (billingResult.responseCode == BillingClient.BillingResponseCode.OK && purchases != null) {
for (purchase in purchases) {
if (purchase.purchaseState == Purchase.PurchaseState.PURCHASED) {
// Don't pass price, products list, or order ID. Session-scoped is enough.
Respectlytics.track("paywall_purchase")
}
}
}
}
}Use this in conjunction with your `BillingClient` setup. The same pattern works with the Google Play Billing Library v6+ — the relevant state is `PURCHASED`, regardless of acknowledgement state.
✦ Privacy & implementation notes
Most analytics SDKs default to tying purchase events to a persistent `user_id` or device-level identifier. Respectlytics's `session_id` rotates every two hours, so a paywall purchase becomes "a purchase happened in this session" — sufficient for funnel analysis, insufficient for resale or cross-app re-targeting. This is the data-minimization trade-off in one line.
The natural aggregation bucket is **(country, platform, day)**. "78% of paywall views convert in DE on iOS today" is a useful comparison even without per-user identity. Most paywall A/B-test decisions are made on differences this granular — going down to per-user is operationally expensive and rarely changes the conclusion.
Many teams discover the `com.google.android.gms.permission.AD_ID` permission in their merged manifest only after Google Play flags them — usually because a transitive dependency dragged it in. Respectlytics's Kotlin SDK has no Google Play Services dependency at all, so it cannot contribute to that merge.
The SDK is implemented as pure Kotlin coroutines with no Java sources, no RxJava, and no platform channels. Events are queued in a `Channel<Event>` buffered to a small ring (RAM-only), drained by a coroutine that flushes every 30 seconds or on backgrounding. There is no SharedPreferences usage.
⇋ How this compares to other analytics SDKs
| What gets sent on a paywall purchase | Firebase Analytics (default) | Mixpanel (default) | Respectlytics |
|---|---|---|---|
| IDFA / AAID | Yes (with user consent) | Optional | Never |
| Persistent user ID | app_instance_id | distinct_id | Never |
| Purchase amount / currency | Recommended | Recommended | Rejected by API |
| Product / SKU identifier | Recommended | Recommended | Rejected by API |
| Transaction ID | Recommended | Recommended | Rejected by API |
| IP address stored | Yes | Yes (90-day default) | Used transiently for country, then discarded |
| What you can compute | Per-user LTV, cohort revenue | Per-user LTV, cohort revenue | Session-grouped funnel, country-level conversion rate |
❓ Frequently asked questions
How do we attribute revenue without a user ID?
You don't, at the user level. You attribute by **session, country, and day**. For most product decisions — "is the new paywall design converting more sessions in DE on iOS?" — that's enough. If you need per-user LTV for investor reporting, that lives in your billing system (Stripe, RevenueCat, App Store Connect) — not in your product analytics.
Can we still A/B-test paywall variants?
Yes. Emit different `event_name` values for each variant — e.g. `paywall_purchase_a`, `paywall_purchase_b`. Aggregation buckets them automatically. No randomized user assignment is stored — variant assignment lives in the client until the event fires.
What about refunds and chargebacks?
Out of scope for product analytics. Your billing system already has authoritative refund data, with the user IDs and amounts you legitimately need to act on. Mixing those into your conversion funnel produces double-counted noise — keep them separate.
Will the App Store reject my app for not collecting purchase metadata?
No. Apple's review guidelines do not require you to collect product or price metadata. Your `Receipt` and `transactionIdentifier` already exist on-device and on Apple's servers — duplicating them into your analytics pipeline is a choice, not a requirement.