> ## Documentation Index > Fetch the complete documentation index at: https://docs.classquill.com/llms.txt > Use this file to discover all available pages before exploring further. # Create Message > Send an in-app message into a conversation. `sender_id` must be an accepted member of your org **and** an active participant of the target conversation (404 otherwise) — the API can't impersonate a family member or post into a thread it isn't part of. The message is sent as plain text, visible to everyone in the thread, and the normal bell/email notifications fire. Honours `Idempotency-Key`. ## OpenAPI ````yaml /openapi.json post /v1/messages openapi: 3.1.0 info: title: ClassQuill Public API description: >- REST API for ClassQuill tutoring organisations. Pipe your sessions, invoices, payments, tutor earnings, students, and more into your own tools. Most endpoints are reads; a focused set of writes (each gated by a *:write scope) create or update data, including creating student/tutor/parent accounts. Authenticate every request with an org API key: Authorization: Token token=ei_live_... Mint keys in the ClassQuill app under Settings → Developers. version: 1.0.0 servers: [] security: - ApiKeyAuth: [] tags: - name: General - name: Sessions - name: Tutors - name: Students & Parents - name: Billing - name: Curriculum - name: Coursework - name: Operations - name: Pricing - name: Bookings - name: Blog - name: Reports paths: /v1/messages: post: tags: - General summary: Create Message description: >- Send an in-app message into a conversation. `sender_id` must be an accepted member of your org **and** an active participant of the target conversation (404 otherwise) — the API can't impersonate a family member or post into a thread it isn't part of. The message is sent as plain text, visible to everyone in the thread, and the normal bell/email notifications fire. Honours `Idempotency-Key`. operationId: create_message_v1_messages_post parameters: - name: Idempotency-Key in: header required: false schema: anyOf: - type: string - type: 'null' title: Idempotency-Key requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/MessageCreate' responses: '201': description: Successful Response content: application/json: schema: $ref: '#/components/schemas/Message' '401': description: Missing, malformed, revoked, or expired credentials. content: application/json: schema: $ref: '#/components/schemas/ApiError' '403': description: The credential lacks the scope this endpoint requires. content: application/json: schema: $ref: '#/components/schemas/ApiError' '422': description: Validation error — `error.details.errors` lists the fields. content: application/json: schema: $ref: '#/components/schemas/ApiError' '429': description: >- Rate limit exceeded — honour Retry-After and the RateLimit-* headers. content: application/json: schema: $ref: '#/components/schemas/ApiError' components: schemas: MessageCreate: properties: conversation_id: type: string title: Conversation Id sender_id: type: string title: Sender Id content: type: string maxLength: 10000 minLength: 1 title: Content reply_to_id: anyOf: - type: string - type: 'null' title: Reply To Id additionalProperties: false type: object required: - conversation_id - sender_id - content title: MessageCreate description: >- POST /v1/messages → send an in-app message into a conversation. `sender_id` must be an accepted org member who is an active participant of the conversation. The message is always inserted as `message_type='text'`, `visibility='everyone'` (so the existing notify/email/mirror triggers fire normally); system/private message types are not settable via the API. Message: properties: id: type: string title: Id conversation_id: anyOf: - type: string - type: 'null' title: Conversation Id sender_id: anyOf: - type: string - type: 'null' title: Sender Id content: anyOf: - type: string - type: 'null' title: Content message_type: anyOf: - type: string - type: 'null' title: Message Type visibility: anyOf: - type: string - type: 'null' title: Visibility reply_to_id: anyOf: - type: string - type: 'null' title: Reply To Id created_at: anyOf: - type: string - type: 'null' title: Created At type: object required: - id title: Message description: >- One message in a thread. Only `visibility='everyone'` (non-deleted) messages are exposed by the read endpoints — family-private (`student_only`/`parent_only`) messages are never returned. ApiError: description: Canonical error envelope for every /v1 error response (4xx/5xx). properties: error: $ref: '#/components/schemas/ApiErrorBody' required: - error title: ApiError type: object ApiErrorBody: description: The `error` object every /v1 error response carries. properties: code: description: >- Stable machine-readable error code: bad_request, unauthorized, forbidden, not_found, conflict, validation_error, rate_limited, or internal_error. examples: - not_found title: Code type: string message: description: Human-readable explanation, safe to surface to end users. examples: - Session not found title: Message type: string status: description: The HTTP status code, repeated in the body. examples: - 404 title: Status type: integer details: additionalProperties: true description: >- Error-specific context. 422 carries the field errors under `errors`; 429 carries `retry_after_seconds`. title: Details type: object required: - code - message - status title: ApiErrorBody type: object securitySchemes: ApiKeyAuth: type: apiKey in: header name: Authorization description: Org API key as `Token token=ei_live_...` ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.