> ## Documentation Index > Fetch the complete documentation index at: https://docs.useboom.ai/llms.txt > Use this file to discover all available pages before exploring further. # Add participants > Add people to an active WhatsApp initiative. WARNING: each person added receives a real outbound WhatsApp message. Do-Not-Contact people are skipped. ## OpenAPI ````yaml /api-reference/openapi.json post /api/v1/initiatives/{id}/participants openapi: 3.1.0 info: title: Boom API version: 1.0.0 description: >- Boom's public REST API — one uniform surface over every platform capability. CDP: upsert people and custom objects, define object and relationship types, link and unlink relationships, and record behavioral events — one record per request or up to 1000 per request via the `/batch` endpoints. Segments: read (list, read, membership) and full authoring — discover the filterable catalog, validate a filter, create and update segments, preview match counts, and trigger evaluation. Initiatives: create and configure outreach initiatives, link WhatsApp templates, drive the lifecycle (launch, cancel, archive), and read collected-data summaries. Participants: enroll people into an active initiative, track their status, read conversation transcripts, and stop outreach. Journeys: read-only access to always-on message flows and their metrics. WhatsApp templates: list your WhatsApp numbers and list, read, and create message templates. The same capabilities are exposed as MCP tools with identical schemas. servers: - url: https://www.useboom.ai description: Production - url: https://dev.useboom.ai description: Development (sandbox — use a development organization API key) security: - bearerAuth: [] paths: /api/v1/initiatives/{id}/participants: post: tags: - Initiatives summary: Add participants description: >- Add people to an active WhatsApp initiative. WARNING: each person added receives a real outbound WhatsApp message. Do-Not-Contact people are skipped. operationId: initiatives_participants_add parameters: - name: id in: path required: true schema: $schema: https://json-schema.org/draft/2020-12/schema type: string minLength: 1 description: Initiative id. requestBody: required: true content: application/json: schema: $schema: https://json-schema.org/draft/2020-12/schema type: object properties: people: minItems: 1 maxItems: 500 type: array items: type: object properties: externalId: type: string minLength: 1 maxLength: 255 description: >- Stable unique identifier for this person in your system (CDP identity key). phoneNumber: type: string minLength: 1 maxLength: 20 description: >- Phone number in E.164 format, e.g. +5215512345678 — the WhatsApp recipient. name: description: First name. type: string minLength: 1 maxLength: 255 lastName: description: Last name. type: string minLength: 1 maxLength: 255 context: description: >- Per-person context values. Keys must match the initiative's context schema. type: object propertyNames: type: string maxLength: 100 additionalProperties: type: string maxLength: 1000 required: - externalId - phoneNumber description: The people to add. Each receives a real WhatsApp message. required: - people responses: '201': description: Success content: application/json: schema: $schema: https://json-schema.org/draft/2020-12/schema type: object properties: data: type: array items: type: object properties: participantId: type: string phoneNumber: type: string status: type: string enum: - ACTIVE - COMPLETED - STOPPED - EXPIRED - FAILED description: >- ACTIVE (conversation may still happen), COMPLETED, STOPPED (messaging halted), EXPIRED, or FAILED. required: - participantId - phoneNumber - status additionalProperties: false errors: type: array items: type: object properties: index: type: number description: Index of the person in the request `people` array. error: type: object properties: code: type: string description: >- One of: contact_suppressed, invalid_phone_number, unknown_context_key, enrollment_failed. message: type: string required: - code - message additionalProperties: false required: - index - error additionalProperties: false required: - data - errors additionalProperties: false '400': description: Validation failed or the request cannot proceed. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '401': description: Missing, malformed, or revoked API key. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '404': description: The resource does not exist in this organization. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '409': description: >- Conflicts with the current state (duplicates, wrong lifecycle state). content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '422': description: The request is well-formed but semantically invalid. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '429': description: Rate limit exceeded — retry after `Retry-After`. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '500': description: Internal server error. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error '503': description: Transient error — retry with a narrower request. content: application/json: schema: type: object properties: error: type: object properties: code: type: string description: Stable machine-readable error code (snake_case). message: type: string required: - code - message required: - error components: securitySchemes: bearerAuth: type: http scheme: bearer description: 'Organization API key, sent as `Authorization: Bearer boom_org_...`.' ````