Incoming Calls Not Reaching Me (iOS / Android)

If the app doesn't ring for incoming calls when it's in the background or the screen is locked, this is almost always a notification/permissions issue rather than a calling problem — the call is arriving at the PBX, but the alert isn't reaching your device.

iOS

Go to Settings → Notifications and confirm DT Communicator has notifications allowed.
Make sure you didn't decline the notification permission prompt during first-time setup — if you did, you'll need to re-enable it in Settings, since iOS won't ask again automatically.
Incoming calls use Apple's VoIP push system, which works even when the app is fully closed (not just backgrounded) — so this genuinely points at a permissions issue rather than needing to keep the app open.

Android

Check the app has notification permission in your device's Settings → Apps → DT Communicator → Notifications.
Check the app isn't restricted by battery optimisation — some manufacturers (Samsung, Xiaomi, Huawei, and others) are particularly aggressive about killing background apps. Look for a setting like "battery optimisation," "app sleep," or "auto-start management" and make sure DT Communicator is excluded/allowed to run in the background.
If you're on a very tightly locked-down work device (MDM-managed), some of these restrictions may be enforced by your organisation's IT policy rather than something you can change yourself.

Still not working?

Contact your administrator with your extension number and device platform — they can check whether push notifications are actually being sent from the server side, which narrows down whether the issue is your device's settings or something further upstream.