Supported Sinch APIs

Sinch Functions provides pre-initialized Sinch SDK clients through the function context. Except for context.voice, clients are only available when their required environment variables are present — accessing an unconfigured client returns null (C#) or undefined (Node.js).

API Availability by Runtime

API	Node.js	C#	Required Config
Voice (v2)	`context.voice`	`context.Voice`	Base credentials only. Always present; calls fail without them
Voice v1	`context.voice.v1`	`context.Voice.V1`	`VOICE_APPLICATION_KEY` + `VOICE_APPLICATION_SECRET`
Conversation	`context.conversation`	`context.Conversation`	`CONVERSATION_APP_ID`
SMS	`context.sms`	`context.Sms`	`SMS_SERVICE_PLAN_ID`
Numbers	`context.numbers`	`context.Numbers`	`ENABLE_NUMBERS_API=true`
Verification	N/A	`context.Verification`	`VERIFICATION_APPLICATION_ID` + `VERIFICATION_APPLICATION_SECRET`
Fax	Via CLI only	Via CLI only	Managed by `sinch` CLI
SIP Trunking	Via CLI only	Via CLI only	Managed by `sinch` CLI
ElevenLabs	`context.elevenlabs` (template helper)	Template helper	`ELEVENLABS_API_KEY`

Base Credentials

All Sinch API integrations require these base credentials:

Variable	Description
`PROJECT_ID`	Your Sinch project ID
`PROJECT_ID_API_KEY`	Project-scoped API key
`PROJECT_ID_API_SECRET`	Project-scoped API secret

Set automatically when you run sinch auth login.

Environment Variables Reference

Base (always required)

Variable	Description
`PROJECT_ID`	Sinch project ID
`PROJECT_ID_API_KEY`	Project API key (key ID)
`PROJECT_ID_API_SECRET`	Project API secret

Voice API

Variable	Description
`VOICE_SERVICE_ID`	Voice API v2 service the function is bound to. `sinch functions init` writes it when you pick or create a service, and deploy points that service's webhook at the function. In Node.js, outbound `context.voice` calls also go through this service
`VOICE_SERVICE_SECRET`	Optional. Signing secret of that service; deploy sets it, so leave it out of `.env`. When `WEBHOOK_PROTECTION` calls for a check, the runtime verifies inbound Voice API v2 webhooks with it; while it is unset (local runs, or a deploy that could not read the service), they are accepted with a one-time warning. To run locally against real calls, set it from `serviceSecret` on `GET /v2/projects/{projectId}/services/{serviceId}`
`WEBHOOK_PROTECTION`	When to verify webhook signatures: `deploy` (default: on the deployed function only), `always`, or `never`. C# reads the `WebhookProtection` setting instead, at the top level or under `Security`
`VOICE_APPLICATION_KEY`	Voice API v1 only (`context.voice.v1`): application key
`VOICE_APPLICATION_SECRET`	Voice API v1 only (`context.voice.v1`): application secret

Conversation API

Variable	Description
`CONVERSATION_APP_ID`	Conversation application ID
`CONVERSATION_REGION`	Region: `US` (default), `EU`, or `BR` — C# only

SMS API

Variable	Description
`SMS_SERVICE_PLAN_ID`	SMS service plan ID

Numbers API

Variable	Description
`ENABLE_NUMBERS_API`	Set to `true` to enable

Verification API (C# only)

Variable	Description
`VERIFICATION_APPLICATION_ID`	Verification application ID
`VERIFICATION_APPLICATION_SECRET`	Verification application secret

ElevenLabs

Variable	Description
`ELEVENLABS_API_KEY`	ElevenLabs API key
`ELEVENLABS_AGENT_ID`	Agent ID for Conversational AI
`ELEVENLABS_AUTO_CONFIGURE`	Set to `true` to auto-configure webhook during tunnel start

Runtime internals (set automatically)

Variable	Description
`API_URL`	Internal API URL (set by the platform)
`FUNCTION_ID`	Function ULID (set by the platform)
`PORT`	HTTP port (default: `3000`)
`VERBOSE`	Set to `true` for detailed runtime logging

Notes

Clients are lazily initialized and cached on first access. Changing environment variables at runtime does not re-initialize clients.
The @sinch/sdk-core package underpins all Node.js clients. The Sinch NuGet package underpins all C# clients.

Configuration & secrets — where to set these variables
Context object — using the clients from your handler