Why does my 'Platform is iOS' segment show 0 users even though I have active iOS devices?

If a "Platform is iOS" segment returns zero users while you clearly have iOS devices, the usual cause is that no iOS device has a valid push token recorded in Pushwoosh — either because registration never reached Pushwoosh, or because the tokens were invalidated and the devices unsubscribed.

What the gateway setting does and does not do

A common misconception is that a Sandbox/Production mismatch blocks registration. It does not. Apple issues the device token to your app on the device; Pushwoosh's gateway setting is only used when Pushwoosh sends. A mismatch therefore shows up at send time as an InvalidToken error — and because Pushwoosh unsubscribes devices that return InvalidToken, a persistent mismatch will steadily empty your iOS audience, which looks like the segment "going to zero".

How to resolve this

1. Confirm devices are reaching Pushwoosh at all. Open the project details and compare Total devices (registered, with or without a push token) against enabled devices (those that hold a push token). If Total devices is also zero, the SDK is not registering — check the app code and the Device API token, not the gateway.
2. Match the APNs Gateway to your build. In Settings > Platform configuration > iOS, set the Gateway to Production for App Store / TestFlight builds and Sandbox for development builds. A single Sandbox & Production certificate can serve both; you pick the gateway here.
3. Verify the credential. Make sure the .p12 certificate or .p8 key belongs to the same App ID / bundle identifier as the build and has not expired or been revoked.
4. Check the sending errors report for InvalidToken, BadDeviceToken or DeviceTokenNotForTopic. These confirm a gateway or bundle-identifier mismatch and explain why previously registered devices disappeared.
5. Re-register test devices after fixing the configuration; devices unsubscribed by an InvalidToken are not restored automatically.

Note for In-App / Web pop-up users

Devices without a push token still count as Total devices and remain reachable with In-App messages, but they carry no push platform tag, so a "Platform is iOS" segment will not see them. Register devices for notifications (you can do this without showing the iOS permission prompt until you are ready) if you need them to be segmentable by platform.