> ## Documentation Index > Fetch the complete documentation index at: https://docs.thinnest.ai/llms.txt > Use this file to discover all available pages before exploring further. # Send Message > Sends one approved template to one number and records it in that customer's conversation. Marketing templates are refused for a customer who opted out; utility and authentication templates are not, since an order confirmation is not something a customer opts out of. Each send is charged like any WhatsApp template from your number, and the Free plan stops at its included messages. At most 60 sends a minute per workspace; send an `Idempotency-Key` so a retry never sends twice. Needs a **full** key. ## OpenAPI ````yaml /api-reference/openapi.json post /messages openapi: 3.1.0 info: title: ThinnestAI API version: 1.0.0 description: >- Build voice and WhatsApp agents, place calls, message customers and run a platform of your own customers on one API. servers: - url: https://app.thinnest.ai/api/v1 description: Production security: - bearerAuth: [] tags: - name: Agents description: >- An agent is one assistant with its instructions, model, languages, website widget and call settings — the same thing the console's Agent page builds. Create one here, then give it knowledge, actions and channels. - name: Knowledge description: >- The documents an agent searches and cites when it answers — a web page or pasted text, split into passages and indexed. Use it for facts (prices, policies, opening hours) rather than putting them in the instructions. - name: Actions description: >- Calls to your own HTTPS API that an agent can make mid-conversation, with arguments it fills from what the customer said — how an agent uses data that stays in your own system. Create one, test it, then switch it on. - name: Tools description: >- Everything else an agent can do besides answer: its built-in tools, the MCP tool servers it is connected to, and the accounts it works in (calendar, spreadsheets, CRMs, records kept here, helpdesks). Every tool starts off. - name: Channels description: >- Where an agent answers: the website widget, WhatsApp, Telegram and calls. Read an agent's channels here and connect a Telegram bot; WhatsApp is connected in the console, because Meta's sign-up runs in the business owner's own browser. - name: Calls description: >- A call is one phone, web or WhatsApp conversation with an agent — one you placed through the API, a campaign's, or one a customer made to you. Place calls here, one at a time or in a batch, and read each one back with its summary, collected details and transcript. - name: Post-call description: >- What happens after a call ends: the outcome, a short summary and the details the agent collects. Read a call's analysis here, and set what an agent does after every call. - name: Recordings description: >- A call's audio, for agents that record their calls. Fetch it with your key, or hand a CRM user the signed link a call report carries — that one needs no key. - name: Conversations description: >- A conversation is one customer's thread with your workspace on one channel — WhatsApp, the web widget, Telegram, voice or email. Read threads and their messages (including to catch up on a webhook you missed), answer a WhatsApp customer from your own agent platform, and resolve, take over or assign threads as the inbox does. - name: Messages description: >- Send one approved WhatsApp template to one customer, because something happened in your own system — an order confirmation, a delivery update, an appointment reminder. No agent is needed: this is how your software starts a WhatsApp conversation. - name: One-time codes description: >- Deliver a login or verification code you generated over WhatsApp, without handling templates yourself, and set up the authentication templates it sends with. WhatsApp writes these messages — "*394812* is your verification code." — so you choose only the expiry, the security line and the button. - name: Contacts description: >- The people your workspace knows — kept in step with your CRM by phone number and your own `externalId`, with marketing consent recorded alongside where it came from. - name: Do not call description: >- Numbers your agents must never ring. Every outbound call refuses a number on this list — Create Call answers `409`, a batch refuses that entry, a calling campaign skips the person and records why, and a booked callback is given up — while inbound calls from it are answered as usual. The same list as **Contacts → Do not contact** in the console, and the one your voice agent adds to on its own when a caller asks not to be called again (in any language), which also sends the `contact.opted_out` webhook event. - name: Events description: >- Tell us something happened in your system — `order.delivered`, `trial.ended` — and the sequences and tags you set up in the console decide what follows. Your code says what happened; the console says what happens next. - name: Templates description: >- WhatsApp message templates: the pre-approved messages your business may send to a customer first, or outside the 24 hours after they last wrote. A template is saved as a draft, sent to WhatsApp for review, and can be sent (Send Message, Create Campaign) only once it is `approved`. Templates are named, not numbered, and one name can exist in several languages. - name: Campaigns description: >- A campaign sends one thing to many people. It is either a WhatsApp **broadcast** (`kind: "whatsapp"`), which sends one approved template to everyone in its audience, or a **calling campaign** (`kind: "voice"`), where an agent phones each person from its own number within the hours you set. Who is in the audience is decided by consent, exactly as in the console, and every campaign is created as a draft that you then launch, schedule, pause, resume or cancel. - name: Sequences description: >- A sequence sends one person several approved WhatsApp templates over days — "your order shipped", then "how was it?" two days later — and stops by itself when they reply, are tagged, or an event says so. People join by tag, by event, or one at a time through Enrol in Sequence. Sequence ids are bare uuids. - name: Forms description: >- A WhatsApp form is a screen your customer fills in without leaving the chat — a delivery address, an appointment request, a short survey. Build it here, publish it to your own WhatsApp Business Account, then send it from a template's button, an agent, the inbox or Reply to Conversation. - name: Phone numbers description: >- The numbers your agents answer and call from. A workspace holds them two ways: numbers it **rents** here, charged every month from your balance, and numbers it **brings** from its own carrier account, which we never bill. Each number is answered by at most one agent (its line) and may be lent to one agent to call out on. A number is named by the number itself, in any spelling: `918041234567`, `+918041234567` and `%2B918041234567` in a path are the same number. - name: Voices description: >- The voices an agent can speak with, as the console's voice picker lists them. An item's `id` is what an agent's `voice.voice` takes. - name: Voice clones description: >- Your workspace's own cloned voices, made from a short recording with the speaker's consent. A clone is listed with the Studio voices and can be put on an agent like any other voice. - name: Models description: >- The language models an agent can answer with, as the console names them. An item's `id` is what an agent's `model` takes. - name: Bring your own keys description: >- Run your agents on your own provider accounts and pay a flat platform fee instead of our usage rates. Bring all three keys (speech-to-text, LLM, voice): ₹0.02 a chat reply and ₹1 a call minute, all-in. Or bring only your voice key (scope voice): our speech-to-text, model and telephony, a call billed at the voice-only BYOK rate (₹1.50 / $0.02 a minute by default), chat replies as usual. There is no fallback to our providers when one of your keys fails. - name: Webhooks description: >- Endpoints an agent's events are sent to as they happen — a CRM, a sheet, Slack, Zapier, or a helpdesk email address. Each delivery is a signed JSON `POST` of `{ "id", "event", "sentAt", "data" }`. **Headers on every attempt** | Header | What it is | |---|---| | `x-thinnest-signature` | `sha256=` under the endpoint's signing secret. | | `x-thinnest-signature-v2` | `sha256=.">` — the delivery time, signed. | | `x-thinnest-delivered-at` | When this attempt left (ISO 8601). | | `x-thinnest-event-id` | `evt_…`, the same as the body's `id` — stable across every retry and re-send. | | `x-thinnest-attempt` | `1` for the first attempt, then `2`, `3`, … | **Retries.** A delivery that fails — any answer other than 2xx, a timeout after 10 seconds, or an address we cannot reach — is tried again after 1 minute, 5 minutes, 30 minutes, 2 hours and 6 hours (six attempts over about 8½ hours). Every attempt sends the **same bytes**, so `sentAt` is when the event happened, not when the attempt left. Payloads are kept for 7 days; within that time any failed delivery can be sent again with Redeliver Webhook Events. **Dedupe** on `x-thinnest-event-id` (or the body's `id`): a retry after a timeout can reach you after you already processed the first attempt. Answer 2xx quickly and do the work afterwards. **Freshness.** To refuse replayed requests, verify `x-thinnest-signature-v2` and reject an `x-thinnest-delivered-at` more than five minutes from your clock. Do not check freshness on `sentAt`: a retry's `sentAt` is hours old by design. **Switch-off.** An endpoint is switched off after five events in a row that each failed every attempt — single failed attempts that later succeed do not count. Events that happen while it is off are recorded as not sent; switch it back on and re-send them. The events an endpoint can subscribe to: | Event | When it fires | |---|---| | `lead.captured` | The agent collected a name, email or phone from somebody who showed real interest. | | `conversation.escalated` | The agent handed a conversation to a person — asked for, or because it could not answer. | | `conversation.resolved` | A teammate marked a conversation done; `data.conversationId` is its `conv_…` id, as Get Conversation takes it. | | `call.completed` | A call the agent placed or answered ended — how it ended and how long it lasted, sent the moment it ends. | | `call.analysed` | A call's results are ready: its summary, the details it collected, the transcript, a recording link and what the call cost (`costMicro`, `currency`) — the same shape as Get Call. | | `campaign.finished` | Every person on a broadcast or a calling campaign has been reached, or given up on. | | `contact.opted_out` | During a call, somebody asked not to be called again; their number (`data.phone`) is now on the do-not-call list. | - name: Usage description: >- Read what your workspace used and spent — replies, calls, WhatsApp, the balance history and invoices — the same figures as the console's Usage and Billing pages. All reads. - name: Analytics description: >- The Dashboard's counts and each agent's Analytics page, for building a dashboard of your own that agrees with the console. - name: Customers description: >- Workspaces you create for your own customers when you build a product on this API. Each customer has its own agents, contacts, knowledge, phone numbers and WhatsApp; your one key reaches any of them by adding `Thinnest-Workspace: ` to a request, and everything they use is charged to you. Manage customers from your own workspace, without that header. - name: Workspace description: >- Your workspace's own settings — its name and time zone — as Settings → General shows them. With `Thinnest-Workspace`, the customer's workspace instead. - name: Projects description: >- Projects group a workspace's agents, and are what a team's access is scoped by. Every workspace has a default project that cannot be deleted; a second project needs a plan with teams and projects. - name: Teams description: >- Teams are groups of members and the projects they can reach. A project granted to no team is open to the whole workspace; granting it to a team restricts it to that team's members (owners and admins always see everything), and removing its last grant opens it up again. - name: Members description: >- The people in your workspace and their roles. An API key acts as an admin, never an owner: it can make people admins or members and remove them, but cannot make anybody an owner, and the last owner can be neither demoted nor removed. - name: Invitations description: >- Invitations to join your workspace, as Settings → Members sends them: an email with a link that works for 14 days. Pending invitations count towards your plan's seats. - name: Notifications description: >- What each kind of notification does in your workspace: shown in the console's feed or muted, and whether it is emailed through the email sender you connected in the console. - name: Saved replies description: >- Sentences your team sends often, offered in the inbox composer as `/shortcut`. paths: /messages: post: tags: - Messages summary: Send Message description: >- Sends one approved template to one number and records it in that customer's conversation. Marketing templates are refused for a customer who opted out; utility and authentication templates are not, since an order confirmation is not something a customer opts out of. Each send is charged like any WhatsApp template from your number, and the Free plan stops at its included messages. At most 60 sends a minute per workspace; send an `Idempotency-Key` so a retry never sends twice. Needs a **full** key. operationId: sendMessage parameters: - $ref: '#/components/parameters/IdempotencyKey' - $ref: '#/components/parameters/Workspace' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/MessageSendRequest' example: to: +91 98765 43210 template: order_confirmation_v1 language: en variables: - Priya - '#10432' - Tuesday buttonVariables: - '10432' responses: '200': description: >- WhatsApp accepted the message — not yet that it arrived; delivery and read are reported afterwards. A replay of an `Idempotency-Key` that already succeeded answers the same with `deduplicated: true` and an `Idempotent-Replayed: true` header. headers: Idempotent-Replayed: description: >- `true` when this is the stored answer to an earlier request with the same `Idempotency-Key`. schema: type: string enum: - 'true' content: application/json: schema: $ref: '#/components/schemas/MessageSent' example: ok: true messageRef: wamid.HBgMOTE5ODc2NTQzMjEwFQIAERgSQjM2RDVGMEU4QzA3RjE2QTYA '400': description: >- The body is not JSON, `to` or `template` is missing, or the number cannot be read. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: >- That number could not be read — too short to be a phone number. '401': $ref: '#/components/responses/Unauthorized' '402': description: >- The Free plan's WhatsApp messages are used up. Switching to pay-as-you-go lifts it. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: >- The Free plan includes 200 WhatsApp messages, and they are used. Switch to Pay as you go — there is no monthly fee — to keep sending. '403': $ref: '#/components/responses/Forbidden' '404': description: >- No template of that name, or it is not approved in the language you asked for — then `available` lists the languages it is approved in. content: application/json: schema: $ref: '#/components/schemas/MessageRefusal' example: error: That template is not approved in hi. available: - en - mr '409': description: >- The state of things refuses it, and retrying unchanged will not help: the template is not approved yet, WhatsApp is not connected (or the number's connection was never finished), sending is restricted on the number, the customer opted out of marketing messages, the template carries something a send cannot fill (such as a media header with no picture), or a request with the same `Idempotency-Key` is still in flight. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: That customer has opted out of marketing messages. '429': description: >- Over 60 sends a minute for this workspace. Wait for `Retry-After` seconds. headers: Retry-After: schema: type: integer description: Seconds to wait. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: Over 60 messages a minute. Slow down and retry. '502': description: >- WhatsApp refused the message, in its own words. Often transient; read the sentence before retrying. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: (#131026) Message undeliverable '503': description: WhatsApp sending is not available right now. Retry later. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: WhatsApp is not configured on this deployment. components: parameters: IdempotencyKey: name: Idempotency-Key in: header required: false description: >- Any unique string. A retry with the same key within 24 hours returns the first request's answer instead of acting twice. schema: type: string maxLength: 255 Workspace: name: Thinnest-Workspace in: header required: false description: >- Developers only: the customer workspace this request acts in — its `org_…` id from `POST /customers`. Leave it out to act in your own workspace. schema: type: string example: org_3fKq9TzQ1mN8vB2xR7cLpA schemas: MessageSendRequest: type: object required: - to - template properties: to: type: string description: >- The customer's number. Include the `+` and the country code (a leading `00` works too); spaces are fine. Without a `+`, a number of ten digits or fewer — or one starting with `0` — is read as an Indian number and `91` is added, so a foreign number sent bare goes to the wrong country. example: +91 98765 43210 template: type: string description: >- The name of an approved template in your workspace. Templates are named, not given by id, so the name stays stable across edits. example: order_confirmation_v1 language: type: string description: >- Which approved language version to send, exactly as approved — `en`, `hi`, `en_US`. Leave it out for the oldest approved version, so adding a language in the console never changes what a working integration sends. example: en variables: type: array items: type: string description: >- Values for the body's `{{1}}`, `{{2}}` … in order. Numbers are sent as text. For an authentication template, the code goes here once — it is copied into the copy-code button for you. example: - Priya - '#10432' - Tuesday buttonVariables: type: array items: type: string description: >- The value for a link button's placeholder. Separate from `variables` because WhatsApp addresses the button on its own. Leave it out on an authentication template. example: - '10432' headerMediaUrl: type: string format: uri description: >- A public link to the picture, video or document for a template with a media header. WhatsApp needs one on every send; leave it out and the template's own stored file is used. example: https://kaapico.in/parcels/10432.jpg formData: type: object additionalProperties: type: string description: >- Pre-fills a WhatsApp form the template's button opens. Only fields the form marked pre-fillable reach the screen; other keys are ignored rather than refused. Values are sent as text. example: order_number: '10432' idempotencyKey: type: string description: >- Same as the `Idempotency-Key` header, for clients that cannot set headers. The header wins when both are sent. MessageSent: type: object required: - ok - messageRef properties: ok: type: boolean const: true description: WhatsApp accepted the message. messageRef: type: - string - 'null' description: >- WhatsApp's own receipt for the message — what delivery and read reports refer to, and what to quote when asking what happened to one. deduplicated: type: boolean description: >- Present, and `true`, only on a replay of an `Idempotency-Key` that already succeeded: nothing was sent this time. Error: type: object required: - error properties: error: type: string description: What went wrong, in a sentence you can show a person. example: error: That agent was not found. MessageRefusal: type: object required: - error properties: error: type: string description: What went wrong, in a sentence you can show a person. available: type: array items: type: string description: >- Only when the template is not approved in the language asked for: the languages it is approved in. responses: Unauthorized: description: The key is missing, wrong or revoked. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: 'Send a valid API key as `Authorization: Bearer `.' Forbidden: description: >- The key's access level (read-only or build) does not allow this request, or the plan does not include it. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: >- This API key is read-only: it can read everything but change nothing. securitySchemes: bearerAuth: type: http scheme: bearer description: >- Your API key (`ta_live_…`) from **Settings → API keys**, sent as `Authorization: Bearer `. Keep it on a server: it can message every customer you have. A key is full, build or read-only; a request its level does not allow is refused with `403`. ```` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.