Sinch In-App Calling

Overview

Real-time voice and video SDK for Android, iOS, and JavaScript (Web). Connects to Sinch's cloud for signaling and routing.

Supported call types

• App-to-App (VoIP/WebRTC between users)
• App-to-Phone (call PSTN numbers)
• App-to-SIP (connect to PBXs, contact centers)
• App-to-Conference (multi-party calls)
• Phone-to-App / SIP-to-App (inbound calls)

Agent Instructions

Prerequisites

The user needs a Sinch account with an application key and secret from the Sinch Build Dashboard.

Integration workflow

1. Detect the platform from the user's project (language, build system, framework):

   • Android (Kotlin/Java, Gradle) → Read references/android.md
   • iOS (Swift/ObjC, Xcode) → Read references/ios.md
   • JavaScript/Web (npm, browser) → Read references/js.md
   • If unclear, ask the user.

2. Walk through the integration steps in the platform reference. Go step by step — confirm each step is in place before moving to the next.

3. Ask about auth approach: Can the Application Secret be embedded (prototyping only) or must JWTs come from a backend (production)?

4. Ask about call types: Which types does the user need? This determines which sections to cover.

5. For Phone-to-App / SIP-to-App: The user needs a backend ICE callback handler. See backend setup below.

Phone-to-App / SIP-to-App backend

Receiving inbound PSTN or SIP calls requires:

1. A Sinch voice number from the Build Dashboard assigned to the app (or SIP origination configured).
2. A callback URL in the app's Voice settings.
3. A backend ICE handler that routes calls via connectMxp:

{
  "action": {
    "name": "connectMxp",
    "destination": {
      "type": "username",
      "endpoint": "target-user-id"
    }
  }
}

Troubleshooting

Symptom	Likely cause	Fix
onClientFailed / clientDidFail	JWT issue — token missing, expired, wrong secret, or malformed	Verify JWT generation: correct app key + secret, kid matches key ID, token not expired. See auth section in platform reference
onClientFailed / clientDidFail	Invalid app key or wrong environment host	Verify key in Dashboard; check environmentHost matches your region
No incoming calls (JS)	Managed push not enabled	Call sinchClient.setSupportManagedPush() before starting — required even for the caller side
No incoming calls (Android)	FCM misconfiguration	Verify FCM credentials in Dashboard ("In-app Voice & Video SDKs" → "Google FCM Identification"); check that the device receives FCM tokens
No incoming calls (iOS)	APNs push not configured or token stale	Verify push certificate/key in Dashboard; ensure registerPushNotificationData is called with a fresh device token
No incoming calls (general)	SinchClient not running on the receiver's device	The receiver's app must have an active, started SinchClient to receive calls. Verify start() completed successfully
App-to-Phone fails immediately	Missing CLI (caller ID)	Set callerIdentifier / cli with a Sinch number
Audio only in foreground (iOS)	CallKit not reporting calls	Report outgoing calls to CallKit for background audio

If the above steps don't resolve the issue, instruct the user to contact Sinch Support with their app key, platform, and a description of the problem.

Public endpoints

Set environmentHost when creating the Sinch client:

Endpoint	Region
ocra.api.sinch.com	Global (auto-routed)
ocra-euc1.api.sinch.com	Europe
ocra-use1.api.sinch.com	North America
ocra-sae1.api.sinch.com	South America
ocra-apse1.api.sinch.com	South East Asia 1
ocra-apse2.api.sinch.com	South East Asia 2

Links

• In-App Calling Overview
• SDK Downloads
• Reference Applications (GitHub)
• Android SDK Reference
• iOS SDK Reference
• JavaScript SDK Reference