> ## Documentation Index > Fetch the complete documentation index at: https://docs.impellabs.tech/llms.txt > Use this file to discover all available pages before exploring further. # Message a customer first > Sends to a customer who has not written first, and opens the conversation, or uses the open one for that number. Answers 201. On Messenger and Instagram the conversation must exist already. Needs the `messages:write` scope. ## OpenAPI ````yaml /openapi/partner.yaml post /api/v1/partner/tenants/{external_ref}/messages/send/ openapi: 3.1.0 info: title: ImpelLabs Partner API version: '1' description: >- The Partner API provisions customer businesses (tenants) and runs their channels, conversations and templates from your own product. Call it from your server with a partner key. Every path ends with a slash. servers: - url: https://api.impellabs.tech security: - bearer: [] tags: - name: Keys description: Your partner API keys. - name: Tenants description: Customer businesses, their channels, conversations and templates. - name: Webhooks description: Where your tenants' events go. - name: WhatsApp sign-up description: The settings of the hosted WhatsApp sign-up. paths: /api/v1/partner/tenants/{external_ref}/messages/send/: post: tags: - Tenants summary: Message a customer first description: >- Sends to a customer who has not written first, and opens the conversation, or uses the open one for that number. Answers 201. On Messenger and Instagram the conversation must exist already. Needs the `messages:write` scope. operationId: post_api_v1_partner_tenants_external_ref_messages_send parameters: - name: external_ref in: path required: true schema: type: string description: Your own id for the customer business, set when you created it. requestBody: content: application/json: schema: type: object properties: to: type: string description: >- The customer phone number, or the Messenger or Instagram customer id. channel: type: string enum: - whatsapp - messenger - instagram description: Default `whatsapp`. whatsapp_number: type: string description: >- The `phone_number_id` to send from. Default is the first connected number. type: type: string description: >- One of `text`, `template`, `image`, `video`, `audio`, `document`, `interactive`, `location`, `reaction`. Default `text`. text: type: string description: The message text. Required for `text`. reply_to: type: string description: A message id or provider message id to quote. template_name: type: string description: The approved template to send. Required for `template`. lang: type: string description: The template language. Default `en_US`. body_params: type: array items: type: string description: The values for the template body. components: type: array items: type: object description: Template components, as Meta defines them. link: type: string description: A public link to the file, for a media type. media_id: type: string description: >- A provider media id, for a media type. Send `link` or `media_id`. caption: type: string description: A caption for a media type. 1024 characters at most. filename: type: string description: A file name for a document. payload: type: object description: For `interactive`, `location` and `reaction`. tag: type: string description: 'Messenger only: `HUMAN_AGENT`.' required: - to example: to: '+15550100101' channel: whatsapp type: template template_name: appointment_reminder lang: en_US body_params: - Sam - 3 pm required: true responses: '201': description: Success content: application/json: example: message: id: 9b3c1d5f-0000-4000-8000-000000000000 object: message role: user type: text text: Hello created_at: '2026-01-15T10:04:00+00:00' conversation: 5d2f7a3e-0000-4000-8000-000000000000 channel: name: whatsapp from: '+15550100101' conversation: id: 5d2f7a3e-0000-4000-8000-000000000000 object: conversation status: active agent: null agent_version: null channel: whatsapp external_ref: null turns: 3 metadata: {} created_at: '2026-01-15T10:00:00+00:00' updated_at: '2026-01-15T10:05:00+00:00' contact: name: Sam phone: '+15550100101' lead_id: 8a1e0c7b-0000-4000-8000-000000000000 human_control: 'on': false reason: '' since: '' state: ai pending_since: '' window: open: true last_inbound_at: '2026-01-15T10:04:00+00:00' closes_at: '2026-01-16T10:04:00+00:00' capabilities: can_text: true can_template: true can_media: true window_open: true window: open: true tags: [] whatsapp_number: '100000000000001' '400': $ref: '#/components/responses/Invalid' '401': $ref: '#/components/responses/Unauthorized' '403': $ref: '#/components/responses/Forbidden' '404': $ref: '#/components/responses/NotFound' 4XX: description: The request is not valid or not allowed content: application/json: schema: $ref: '#/components/schemas/Error' components: responses: Invalid: description: >- A field is missing or wrong. The body names each field: {"field": "what to fix"}. Unauthorized: description: The credentials are missing, wrong, expired or revoked. Forbidden: description: These credentials may not do this. NotFound: description: There is no such row, or these credentials cannot see it. schemas: Error: type: object description: >- An error. Most errors carry `detail`. Some carry `error` with `code` and `message`. properties: detail: type: string code: type: string field: type: string error: type: object properties: code: type: string message: type: string securitySchemes: bearer: type: http scheme: bearer ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.