> ## Documentation Index
> Fetch the complete documentation index at: https://hellotars.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Start a conversation

> Start a new conversation at a published chat agent's trigger step.

A trigger step is an entry point in a published chat flow. Send its agent ID, trigger ID and channel identifier.

Each request starts a new conversation. Existing open conversations for the same end user, inbox and channel are abandoned first.

The trigger starts the flow but sends nothing itself. A downstream channel step sends the first message.

The builder's **Sample Request & Testing** panel provides the request for your trigger. **Keys that can start this trigger** lists eligible keys.

## Related pages

* [Authentication](https://hellotars.com/docs/developer/authentication.md)


## OpenAPI

````yaml api-reference/openapi.json POST /api/v1/conversations
openapi: 3.1.0
info:
  title: Tars API
  version: '1'
  description: >-
    Start conversations, send messages, manage contacts, send campaign messages,
    place and read calls, and manage webhook destinations.
servers:
  - url: https://us.api.hellotars.com
    description: United States
  - url: https://eu.api.hellotars.com
    description: European Union
  - url: https://in.api.hellotars.com
    description: India
  - url: https://qa.api.hellotars.com
    description: Qatar
security:
  - bearerAuth: []
tags:
  - name: Conversations
    description: Start conversations at a chat agent's trigger step.
  - name: Messages
    description: Send channel messages as a chat agent.
  - name: Contacts
    description: Read and manage contacts.
  - name: Campaigns
    description: Send webhook campaign messages.
  - name: Calls
    description: Place, read and manage phone calls.
  - name: Agents
    description: Read chat agents and voice agents.
  - name: Phone numbers
    description: Read your phone numbers.
  - name: Artefacts
    description: Download call recordings.
  - name: Webhooks
    description: Manage webhook destinations.
paths:
  /api/v1/conversations:
    post:
      tags:
        - Conversations
      summary: Start a conversation at a trigger step
      description: >-
        Starts a new conversation for one channel user at a chat agent's trigger
        step and runs the agent's published flow from that step. It never
        continues an existing conversation: the user's open conversations on the
        same inbox and channel are abandoned first.


        Requires the Start conversations permission (`conversations:start`).
      operationId: startConversation
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/StartConversation'
      responses:
        '201':
          description: The conversation started.
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Conversation'
        '400':
          description: validation_failed, invalid_json
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '401':
          description: unauthorized, invalid_key
          headers:
            WWW-Authenticate:
              schema:
                const: Bearer
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '403':
          description: >-
            organization_inactive, billing_locked, permission_missing,
            resource_not_allowed
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '404':
          description: not_found
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '405':
          description: method_not_allowed
          headers:
            Allow:
              description: The methods this path accepts.
              schema:
                type: string
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '409':
          description: wrong_region, invalid_state
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '413':
          description: payload_too_large
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '422':
          description: channel_misconfigured
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '429':
          description: rate_limited
          headers:
            Retry-After:
              description: Whole seconds to wait before retrying.
              schema:
                type: integer
                minimum: 1
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
        '500':
          description: internal_error
          content:
            application/problem+json:
              schema:
                $ref: '#/components/schemas/Problem'
      security:
        - bearerAuth: []
components:
  schemas:
    StartConversation:
      type: object
      description: Start a conversation at a trigger step of a chat agent.
      additionalProperties: false
      properties:
        agentId:
          type: string
          maxLength: 128
          description: The chat agent id.
        triggerId:
          type: integer
          minimum: 0
          description: The trigger step's number in the agent's flow.
        channelUserId:
          type: string
          description: >-
            The user's identifier on the trigger step's channel. For WhatsApp,
            the phone number in international format.
        data:
          type: object
          description: Each top-level key becomes a {{trigger.<key>}} variable in the flow.
      required:
        - agentId
        - triggerId
        - channelUserId
    Conversation:
      type: object
      description: The conversation that started.
      properties:
        conversationId:
          type: string
        status:
          const: started
      required:
        - conversationId
        - status
    Problem:
      type: object
      description: >-
        RFC 9457 problem details. Clients switch on code, never on title or
        detail.
      properties:
        title:
          type: string
          description: The catalogue title of code.
        status:
          type: integer
          description: The HTTP status.
        detail:
          type: string
          description: A sentence about this failure, for a developer.
        instance:
          type: string
          description: The request id (req_…). Quote it when you contact support.
        code:
          type: string
          enum:
            - invalid_json
            - validation_failed
            - variable_key_not_allowed
            - invalid_variable_value
            - cursor_expired
            - cursor_mismatch
            - campaign_mode_invalid
            - unauthorized
            - invalid_key
            - session_invalid
            - insufficient_balance
            - organization_inactive
            - billing_locked
            - permission_missing
            - resource_not_allowed
            - entitlement_missing
            - origin_not_allowed
            - recaptcha_failed
            - consent_revoked
            - us_marketing_blocked
            - channel_test_mode
            - quota_exceeded
            - forbidden
            - not_found
            - method_not_allowed
            - wrong_region
            - conflict
            - contact_exists
            - idempotency_key_reuse
            - agent_unavailable
            - call_not_live
            - call_still_live
            - call_content_deleted
            - invalid_state
            - campaign_paused
            - template_version_drift
            - channel_unavailable
            - artefact_deleted
            - campaign_gone
            - payload_too_large
            - template_not_approved
            - channel_misconfigured
            - channel_reauth_required
            - meta_rejected
            - rate_limited
            - concurrency_limit_reached
            - worker_busy
            - meta_rate_limited
            - internal_error
            - upstream_unavailable
            - meta_unavailable
            - worker_not_deployed
            - worker_unavailable
        retryable:
          type: boolean
          description: true when the same request can succeed later.
        errors:
          type: array
          items:
            $ref: '#/components/schemas/ValidationIssue'
        required:
          type: string
          description: The permission the key lacks (permission_missing).
        region:
          type: string
          description: The organization's region (wrong_region).
        field:
          type: string
          enum:
            - email
            - phone
        contactId:
          type: string
          description: The contact that already has the email or phone.
        callId:
          type: string
        reason:
          type: string
      required:
        - title
        - status
        - detail
        - instance
        - code
        - retryable
    ValidationIssue:
      type: object
      description: One field that failed validation.
      properties:
        path:
          type: string
          description: >-
            Dotted path of the field (template.parameters.body.0), the query
            parameter name, or an empty string for the whole body.
        code:
          type: string
          description: >-
            Why the field failed, for example required, unknown_field,
            out_of_range or template_param_missing.
        message:
          type: string
      required:
        - path
        - code
  securitySchemes:
    bearerAuth:
      type: http
      scheme: bearer
      description: >-
        An API key (`tars_sk_…`) sent as `Authorization: Bearer <key>`. Each
        operation names the permission it needs. Create keys in Settings →
        Integrations → API keys.

````

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