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

# Send a reply

> **Send a reply to a lead in an existing conversation thread**

The correct sending inbox is automatically determined from the thread history to
maintain conversation continuity.

After a successful send, all pending sequence follow-ups for this lead are
automatically cancelled.



## OpenAPI

````yaml /public_openapi.json post /api/public/v1/replies/threads/{thread_id}/reply
openapi: 3.0.3
info:
  title: ColdSend Public API
  description: >-
    Programmatic access to ColdSend for managing cold email campaigns and sender
    accounts.
  version: 1.0.0
  contact:
    name: ColdSend Support
    email: support@coldsend.pro
    url: https://coldsend.pro
servers:
  - url: https://api.coldsend.pro
    description: Production
security:
  - ApiKeyAuth: []
paths:
  /api/public/v1/replies/threads/{thread_id}/reply:
    post:
      tags:
        - Replies
      summary: Send a reply
      description: >-
        **Send a reply to a lead in an existing conversation thread**


        The correct sending inbox is automatically determined from the thread
        history to

        maintain conversation continuity.


        After a successful send, all pending sequence follow-ups for this lead
        are

        automatically cancelled.
      operationId: send_reply_api_public_v1_replies_threads__thread_id__reply_post
      parameters:
        - name: thread_id
          in: path
          required: true
          schema:
            type: string
            format: uuid
            description: Thread ID
            title: Thread Id
          description: Thread ID
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/PublicSendReplyRequest'
      responses:
        '201':
          description: Reply queued successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/PublicReplyResponse'
        '401':
          description: Missing or invalid API key
        '403':
          description: Insufficient permissions – requires 'replies:create' scope
        '404':
          description: Thread or lead not found
        '422':
          description: Validation Error
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/HTTPValidationError'
components:
  schemas:
    PublicSendReplyRequest:
      properties:
        body:
          type: string
          nullable: true
          title: Body
          description: Plain-text reply body (required if html_body is not provided)
        html_body:
          type: string
          nullable: true
          title: Html Body
          description: HTML reply body (required if body is not provided)
        attachments:
          items:
            $ref: '#/components/schemas/AttachmentItem'
          type: array
          nullable: true
          title: Attachments
          description: Optional file attachments (max 5, 10 MB total, base64-encoded)
      type: object
      title: PublicSendReplyRequest
      description: Request body for sending a reply to an existing thread.
    PublicReplyResponse:
      properties:
        success:
          type: boolean
          title: Success
        message:
          type: string
          title: Message
        message_id:
          type: string
          nullable: true
          title: Message Id
          description: Tracking message ID
        from_address:
          type: string
          title: From Address
          description: Inbox address the reply was sent from
        to_address:
          type: string
          title: To Address
          description: Lead email address the reply was sent to
        thread_id:
          type: string
          nullable: true
          title: Thread Id
          description: Thread ID
      type: object
      required:
        - success
        - message
        - from_address
        - to_address
      title: PublicReplyResponse
      description: Response returned after sending a reply.
    HTTPValidationError:
      properties:
        detail:
          items:
            $ref: '#/components/schemas/ValidationError'
          type: array
          title: Detail
      type: object
      title: HTTPValidationError
    AttachmentItem:
      properties:
        filename:
          type: string
          maxLength: 256
          title: Filename
          description: Attachment file name
        content_base64:
          type: string
          title: Content Base64
          description: Base64-encoded file content
        content_type:
          type: string
          maxLength: 256
          title: Content Type
          description: MIME content type
          default: application/octet-stream
      type: object
      required:
        - filename
        - content_base64
      title: AttachmentItem
      description: Schema for a single file attachment (base64-encoded).
    ValidationError:
      properties:
        loc:
          items:
            anyOf:
              - type: string
              - type: integer
          type: array
          title: Location
        msg:
          type: string
          title: Message
        type:
          type: string
          title: Error Type
      type: object
      required:
        - loc
        - msg
        - type
      title: ValidationError
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: header
      name: X-API-Key
      description: API key with format cs_live_xxx

````