Calls

A call is one outbound phone call, fired server-to-server. It is the primitive to reach for when your own system decides who to ring and when — a CRM trigger, a queue worker, a workflow step — and you don’t want to model it as a campaign. Each call is a durable record that owns its own retries, calling window and concurrency slot. Your workspace’s calls form a queue: they dial in the order they come due, as concurrency slots free up. Every dial creates a session, so one call can have several sessions attached to it.

Three ways to start a voice conversation, and they are not interchangeable:

POST /calls — one outbound phone call, API key only, no human in the loop. This page.
POST /sessions — a web (browser) call for a signed-in user, or a dashboard test phone call (one test call of either kind at a time per workspace); requires a bearer login and returns a participant_token.
Campaigns — bulk outreach over a recipient list, with scheduling and per-recipient state.

Endpoints

Method	Path	Auth / Scope
POST	`/calls`	`X-API-KEY` only + `sessions:write`
GET	`/calls`	`sessions:read`
GET	`/calls/{call_id}`	`sessions:read`
POST	`/calls/{call_id}/cancel`	`sessions:write`

POST /calls rejects bearer logins and agent-session tokens even though both can carry sessions:write. An agent-session token lives inside every running voice worker for the duration of a call, so accepting one would let the credential minted for a call originate the next one. Use a workspace API key.

Place a call

curl -X POST "$LEHAR_BASE_URL/calls" \
  -H "X-API-KEY: $LEHAR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "agent_id": "agent_sales_hi",
    "to_number": "+919876543210",
    "callee_name": "Jane",
    "custom_variables": { "company": "Acme" },
    "idempotency_key": "crm-lead-8821",
    "call_config": {
      "max_call_length": 600,
      "call_retry_config": { "retry_count": 2, "retry_not_picked": 30 },
      "call_time": { "call_start_time": "10:00", "call_end_time": "19:00", "timezone": "Asia/Kolkata" }
    }
  }'

The agent must be published and channel=voice.

Request fields

The body is a strict allowlist — an unrecognised field is a 400 naming it, so a setting can never appear to take effect when it didn’t.

Field	Required	Notes
`agent_id`	Yes	A published voice agent.
`to_number`	Yes	E.164, e.g. `+919876543210`.
`callee_name`	No	Up to 128 characters. Fills the agent’s built-in `{{callee_name}}` placeholder, spoken in Title Case (`VIKAS AWASTHI` → “Vikas Awasthi”); stored and echoed exactly as sent.
`from_phone_number_id`	No	Caller ID to dial from; defaults to the workspace’s number. See Channels.
`custom_variables`	No	Values substituted into the agent’s prompt. Max 64 keys, scalar values only, 30 KB total.
`metadata`	No	Opaque JSON echoed back to you. Max 16 KiB.
`idempotency_key`	No	1–128 chars of `[A-Za-z0-9_.:-]`.
`call_config`	No	Timeouts, retries and calling window — below.

custom_variables values must be strings, numbers, booleans or null: they are substituted verbatim into the prompt, so a nested object would render as raw data inside the agent’s instructions. The one exception is the built-in {{callee_name}} (see Agents): it is Title-Cased for speech, and when custom_variables.callee_name is absent or blank it comes from the top-level callee_name.

`call_config`

Field	Meaning
`idle_timeout_warning`	Seconds of caller silence, counted from when the agent stops speaking, before the agent nudges. Must be less than `idle_timeout_end`, or the call ends before the nudge can play.
`idle_timeout_end`	Seconds of caller silence before the agent hangs up, counted from when the agent last stopped speaking. The nudge counts as agent speech and restarts this window, so a caller who never replies stays on the line for roughly `idle_timeout_warning` + `idle_timeout_end`.
`max_call_length`	Seconds; caps the whole call. Max 60 minutes (3600). Unset defaults to this ceiling; a higher value is rejected with `400`.
`call_retry_config.retry_count`	Extra dials after the first, `0`–`9`.
`call_retry_config.retry_busy` / `retry_not_picked` / `retry_failed`	Delay before retrying a `busy` / `no_answer` / any other failed outcome, in minutes. Clamped to 1–1440.
`call_time.call_start_time` / `call_end_time`	Permitted calling window, `HH:MM`.
`call_time.timezone`	IANA zone the window is evaluated in. Defaults to `Asia/Kolkata`; a name that isn’t a valid IANA zone is rejected with `400`.

A retry re-checks the calling window, so a backoff can never push a dial outside it. A declined call (the callee actively rejected it) is never retried.

Fields that are refused

Field	Instead
`config`	Publish the agent with the config you want — the published agent is the contract.
`webhook_url`	Register a workspace webhook subscription.
`scheduled_at`	Use `call_config.call_time`.
`call_type`	`POST /calls` always places an outbound phone call.
`campaign_id`	Use the campaigns API.

smart_formatter (extract_first_name, transliteration, transliteration_language) is accepted, stored and echoed back, but not applied to the call. It exists for contract compatibility with migrating integrations; don’t rely on it for behaviour.

Response

POST /calls answers 200 with the call record. Accepting a call is asynchronous — it may still be waiting for its calling window or queued behind your workspace’s concurrency cap — so there is no dispatch id to report yet. Poll GET /calls/{id} or subscribe to call_completed. If call orchestration is briefly unavailable, the call is still accepted as queued and dials once it recovers. That cap counts every live call in the workspace: API calls, campaign dials, inbound calls, and a test call — browser or phone — someone has started from the dashboard. So while a dashboard test call is running, one fewer slot is free for your calls.

{
  "call_id": "call_01EXAMPLE",
  "customer_id": "customer_01EXAMPLE",
  "agent_id": "agent_sales_hi",
  "status": "queued",
  "outcome": null,
  "sub_status": null,
  "error": null,
  "to_number_masked": "+9198****3210",
  "callee_name": "Jane",
  "from_number": "+911140000000",
  "from_phone_number_id": "pn_01EXAMPLE",
  "custom_variables": { "company": "Acme" },
  "call_config": { "max_call_length": 600 },
  "smart_formatter": {},
  "scheduled_for": null,
  "attempt_count": 0,
  "session_id": null,
  "created_at": "2026-08-11T09:00:00Z",
  "updated_at": "2026-08-11T09:00:00Z",
  "completed_at": null
}

The response never echoes to_number — you supplied it, and repeating it would put a subscriber number into every orchestrator’s response logs. to_number_masked is enough to reconcile against your own record. There is no participant_token: this is a phone call, not a browser session.

Lifecycle

queued, scheduled, dialing and in_progress are active; completed, failed and cancelled are terminal. A call waiting for a retry is scheduled, with scheduled_for saying when it may dial again; its outcome stays empty until the call is final. session_id is the latest dialled session. Cancel works from any active status. A queued or scheduled call is never dialled; a call that is ringing or live is hung up. Cancelling a terminal call returns 409.

Inspect a call

GET /calls/{call_id} returns the record above plus one attempts entry per dial:

{
  "call_id": "call_01EXAMPLE",
  "status": "completed",
  "attempt_count": 2,
  "attempts": [
    { "session_id": "session_01A", "status": "failed", "outcome": "no_answer", "sentiment": null, "started_at": "…", "ended_at": "…" },
    { "session_id": "session_01B", "status": "ended", "outcome": "completed", "sentiment": "positive", "started_at": "…", "ended_at": "…" }
  ]
}

Each session_id is a full session — transcript, cost and recording all hang off it. outcome uses the same vocabulary everywhere in the platform: completed, no_media, no_answer, busy, declined, failed, user_disconnected, expired. sentiment is populated only for agents that opted into sentiment analysis. GET /calls lists them, filtered by status, agent_id, created_from and created_to, with standard offset pagination.

Idempotency

Send an idempotency_key and a repeat of the same request is refused with 409 naming the existing call, rather than dialling the number twice. This is the safe way to retry a POST /calls whose response you never saw.

Errors

HTTP	Code	When
400	`invalid_request`	Unknown or malformed field.
402	`insufficient_credits`	Workspace balance is below the invocation threshold, checked when the call is accepted. See Billing.
403	`forbidden`	Not an API-key credential, or the agent isn’t yours.
404	`not_found`	Unknown `call_id` or agent.
409	`conflict`	Duplicate `idempotency_key` (including two requests racing with the same key), or cancelling a terminal call.

The 402 and destination checks run before the call is queued, so no call record is created on refusal. Where a deployment restricts outbound destinations, a to_number outside the permitted prefixes is refused with 400 invalid_request (“to_number is not a permitted destination”).

Outbound webhooks

Get call_completed pushed to you instead of polling.

Sessions

Transcript, cost and recording for each dial.

Get Started

Key Concepts

Guides

Deep Dives

Endpoints

Place a call

Request fields

`call_config`

Fields that are refused

Response

Lifecycle

Inspect a call

Idempotency

Errors

Outbound webhooks

Sessions

​Endpoints

​Place a call

​Request fields

​call_config

​Fields that are refused

​Response

​Lifecycle

​Inspect a call

​Idempotency

​Errors

Outbound webhooks

Sessions

Endpoints

Place a call

Request fields

`call_config`

Fields that are refused

Response

Lifecycle

Inspect a call

Idempotency

Errors