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If AppsFlyer’s S2S Send Event API returns HTTP 200 but an iOS event is missing, check the app_id in the request URL first. For this endpoint, use the App Store numeric ID with the id prefix, such as id123456789. AppsFlyer documents that leaving off the prefix can return 200 OK without recording the event. A 200 response is not proof of ingestion.
Correct the iOS app ID in the S2S URL
The Send Event API endpoint is POST https://api3.appsflyer.com/inappevent/{app_id}. For an iOS app, the path’s {app_id} must be the App Store ID prefixed with id. For example, if the numeric App Store ID is 123456789, the path segment should be id123456789.
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AppsFlyer’s Send Event API reference warns that omitting the prefix can still produce a 200 OK response while the event is not recorded. Inspect the final URL your system sends—not just a configuration value or log entry that may differ from the actual request.
Why HTTP 200 does not confirm event ingestion
AppsFlyer says it performs minimum data validation when a message is received. As a result, an OK response can be returned even when an event is not completely recorded. Treat the status as an acknowledgment from the API, not as an ingestion receipt; verify that the event appears in the relevant AppsFlyer reporting or test workflow.
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Check the request if the prefix is already correct
If the path contains the correct id-prefixed App Store ID, check the other documented requirements rather than assuming the prefix is still the cause.
- App and credential match: Confirm the path’s app ID belongs with the S2S authentication token you are using. AppsFlyer lists an app ID/token mismatch as a possible request error and notes that using a key other than the app’s S2S key can result in an unauthorized response.
- Required event identifier: Include
appsflyer_idin the JSON body and check that its value belongs to the intended app instance. - Valid, correctly formatted JSON: Check the serialized body and its formatting. The API reference sets a 1 KB JSON payload limit.
- One event per request: If the body contains multiple events, send each as a separate request.
- Transport security: Use TLS 1.2 or higher.
These requirements and troubleshooting notes appear in AppsFlyer’s S2S Send Event API reference. The documentation establishes the missing-prefix failure mode, but it cannot identify the cause in a specific integration without the actual URL, body, credentials, and event evidence.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do not copy the S2S format into iOS SDK settings
The identifier format depends on where it is used. In the S2S URL path, the iOS App Store ID needs the id prefix. The SDK troubleshooting instructions use a numeric app ID without that prefix in the SDK configuration example. These are different fields, so do not fix an SDK configuration by copying the S2S path format.
If the missing event comes from the iOS SDK rather than an S2S request, follow AppsFlyer’s iOS SDK troubleshooting guide. It identifies an app ID not found as a possible 404 cause and an authentication or dev-key problem as a possible 400 cause.
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Use this troubleshooting order
- Inspect the actual request URL and confirm its path is
/inappevent/id<numeric App Store ID>for the iOS app. - Confirm the S2S token belongs to that app.
- Check that the body contains a valid
appsflyer_id, is correctly formatted JSON, stays within the 1 KB payload limit, and sends one event per request. - After the request, verify the event in AppsFlyer instead of relying on HTTP 200 alone.
- If the request is actually generated by the iOS SDK, troubleshoot its SDK app ID and credentials using the SDK-specific format.
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