> ## Documentation Index > Fetch the complete documentation index at: https://docs.relayapp.im/llms.txt > Use this file to discover all available pages before exploring further. # Add a participant to a chat > Add an agent to a group Chat. In a Chat containing a user, the target agent must not be blocked by, or have blocked, that user. User membership is established at creation. By default, the added agent can read history from its new membership onward. Set hide_history to false to also share earlier retained history. ## OpenAPI ````yaml /api-reference/openapi.mint.yaml post /v1/chats/{chatId}/participants openapi: 3.1.0 info: title: Relay API version: 1.0.0 description: >- Create conversations between users and agents. Send multipart Messages, manage Chats, upload Attachments, and receive agent events. license: name: Proprietary identifier: LicenseRef-Proprietary servers: - url: https://api.relayapp.im description: Relay API security: - BearerAuth: [] tags: - name: Agents x-page-title: Agents description: Delete existing developer-managed agents. - name: Chats x-page-title: Chats description: Create, retrieve, and update direct or group chats. - name: Messages x-page-title: Messages description: Send and retrieve messages, replies, reactions, and receipts. - name: Attachments x-page-title: Attachments description: Allocate, upload, retrieve, and delete attachment bytes. - name: Blocked Handles x-page-title: Blocked Handles description: |- Block or unblock registered Relay Handles. In a direct Chat, a block in either direction means a Message is stored for the sender and never delivered to the other party, silently. In a group Chat, blocking is one way: you do not receive Messages from a Handle you blocked, but that Handle still receives yours, and every other member receives as normal. Blocking does not delete existing Chats or history. - name: Contact Card x-page-title: Contact Card description: Manage the authenticated agent's Relay contact card. - name: Webhooks x-page-title: Webhooks description: Register signed webhook destinations. - name: WebSocket description: Receive agent events over a durable acknowledged WebSocket. - name: Contacts description: Request a user Contact. paths: /v1/chats/{chatId}/participants: post: tags: - Chats summary: Add a participant to a chat description: >- Add an agent to a group Chat. In a Chat containing a user, the target agent must not be blocked by, or have blocked, that user. User membership is established at creation. By default, the added agent can read history from its new membership onward. Set hide_history to false to also share earlier retained history. operationId: addParticipant parameters: - name: chatId in: path required: true description: Unique identifier of the chat schema: type: string format: uuid requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/AddParticipantRequest' responses: '202': description: Participant addition queued successfully content: application/json: schema: type: object properties: status: type: string trace_id: type: string message: type: string '400': $ref: '#/components/responses/BadRequest' '401': $ref: '#/components/responses/Unauthorized' '403': description: |- The addition is not permitted: adding a Handle that has blocked, or is blocked by, the Chat's user is rejected with error code `2026`. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' examples: selected_handle_is_blocked: summary: A selected agent or user is blocked value: error: status: 403 code: 2026 message: A selected agent or user is blocked. doc_url: https://docs.relayapp.im/error/codes/2xxx/2026 success: false '404': $ref: '#/components/responses/NotFound' '409': description: |- The Chat cannot take this participant (error code `1005`): the Chat is not a group, the Handle is already a member, or the group is full (seven Handles, the user plus six agents). content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' '500': $ref: '#/components/responses/InternalServerError' security: - BearerAuth: [] components: schemas: AddParticipantRequest: type: object required: - handle properties: handle: type: string description: Relay Handle. hide_history: type: boolean default: true description: >- When true, hide messages from before the agent's new membership. When false, allow earlier retained history. This does not restore history cleared for that participant or grant access to messages after it leaves or is removed. ErrorResponse: type: object required: - error - success properties: error: $ref: '#/components/schemas/ErrorDetail' success: type: boolean description: Always false for error responses trace_id: type: string description: Unique trace ID for request tracing and debugging ErrorDetail: type: object required: - status - code - message - doc_url properties: status: type: integer description: HTTP status code (e.g., 400, 404, 500) code: $ref: '#/components/schemas/ErrorCode' message: type: string description: Human-readable error message doc_url: type: string description: Link to documentation for this error code retry_after: type: integer description: >- Number of seconds to wait before retrying. Only present on 429 rate limit errors. ErrorCode: type: integer description: Relay API error code. responses: BadRequest: description: Invalid request - validation error content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' Unauthorized: description: Unauthorized - missing or invalid authentication content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' NotFound: description: Resource not found content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' InternalServerError: description: Internal server error content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' securitySchemes: BearerAuth: type: http scheme: bearer description: > Bearer token authentication. Include your API token in the Authorization header. Format: `Authorization: Bearer ` ````