> ## 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. # Reply to Conversation > Your own agent platform answers a WhatsApp customer — the other half of the `message.received` webhook. Send exactly one of `text`, `media`, `template` or `form`; text, media and forms need the customer's 24-hour window open, a template does not. Only works on a number with **Connect External Agent/CRM** turned on, and not while a teammate has taken the conversation over. Each message is charged like any WhatsApp message from that number. Needs a **full** key. ## OpenAPI ````yaml /api-reference/openapi.json post /conversations/{id}/reply 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: /conversations/{id}/reply: post: tags: - Conversations summary: Reply to Conversation description: >- Your own agent platform answers a WhatsApp customer — the other half of the `message.received` webhook. Send exactly one of `text`, `media`, `template` or `form`; text, media and forms need the customer's 24-hour window open, a template does not. Only works on a number with **Connect External Agent/CRM** turned on, and not while a teammate has taken the conversation over. Each message is charged like any WhatsApp message from that number. Needs a **full** key. operationId: replyToConversation parameters: - name: id in: path required: true description: >- The conversation's id (`conv_…`) — the `conversationId` in the `message.received` delivery. schema: type: string example: conv_8d41f2a7-3c6e-4b19-9f05-6a2e7c1d4b83 - $ref: '#/components/parameters/IdempotencyKey' - $ref: '#/components/parameters/Workspace' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/ConversationReplyRequest' example: text: 'Yes — it left our warehouse this morning. Tracking: AB123456.' responses: '200': description: >- Sent. A replay of an `Idempotency-Key` returns the first answer with an `Idempotent-Replayed: true` header. content: application/json: schema: $ref: '#/components/schemas/ConversationReplyResult' example: ok: true '400': description: No kind, more than one kind, or a field that is not valid. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: >- Send only one of `text`, `media`, `template` or `form` — got text, template. '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: >- The conversation is not in this workspace, the template does not exist or is not approved in that language, no published form has that name, or no form has that id. A template's language refusal also carries `available`, the languages it is approved in. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: No published form called "Delivery address". '409': description: >- The state of the conversation refuses it: External Agent/CRM is off for this number, a teammate has taken it over, the 24-hour window has closed (send a template), the template is not approved, is on another number or cannot be filled, the customer opted out of marketing, the number is disconnected or restricted, the form is not published, two published forms share that name, or a request with the same `Idempotency-Key` is still in flight. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: >- The 24-hour window has closed. Only an approved template can reach this customer now — send `template` instead. '429': $ref: '#/components/responses/TooManyRequests' '502': description: >- WhatsApp refused the message or the form this time. Nothing was sent and the `Idempotency-Key` is released, so retrying with the same key is safe. content: application/json: schema: $ref: '#/components/schemas/Error' example: error: 'WhatsApp refused it: (#131047) Re-engagement message' '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: ConversationReplyRequest: description: >- Exactly one of `text`, `media`, `template` or `form`. Two in one call are refused, so a customer never gets two messages when you meant one. oneOf: - $ref: '#/components/schemas/ConversationReplyText' - $ref: '#/components/schemas/ConversationReplyMedia' - $ref: '#/components/schemas/ConversationReplyTemplate' - $ref: '#/components/schemas/ConversationReplyForm' ConversationReplyResult: type: object required: - ok properties: ok: type: boolean const: true description: WhatsApp accepted it. Delivery and read are reported afterwards. messageRef: type: - string - 'null' description: >- WhatsApp's receipt for a template send. Absent for text, media and forms. 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. ConversationReplyText: type: object title: Text required: - text properties: text: type: string minLength: 1 maxLength: 4096 description: >- The reply, up to 4,096 characters after trimming. Only while the customer's 24-hour window is open. idempotencyKey: type: string description: >- Same as the `Idempotency-Key` header, for clients that cannot set headers. The header wins when both are sent. ConversationReplyMedia: type: object title: Media required: - media properties: media: type: object description: >- A file WhatsApp fetches from your link. Only while the customer's 24-hour window is open. WhatsApp's own size and format limits apply. required: - type - url properties: type: type: string enum: - image - video - audio - file description: What kind of file it is. `file` sends a document. url: type: string format: uri maxLength: 2048 description: A public `https://` link. caption: type: string maxLength: 1024 description: Shown under an image or video. filename: type: string default: file description: >- What a document is called on the customer's phone. Used for `file` only. idempotencyKey: type: string description: >- Same as the `Idempotency-Key` header. The header wins when both are sent. example: media: type: file url: https://kaapico.in/invoices/10432.pdf filename: invoice-10432.pdf ConversationReplyTemplate: type: object title: Template required: - template properties: template: type: object description: >- An approved template on this conversation's number. Works after the 24-hour window has closed too. The same checks as Send Message apply, including opt-outs for marketing templates. required: - name properties: name: type: string description: The template's name. language: type: string description: >- Which approved language version, exactly as approved — `en`, `hi`, `en_US`. Leave it out for the oldest approved version. variables: type: array maxItems: 20 items: type: string maxLength: 1024 description: Values for the body's `{{1}}`, `{{2}}` … in order. buttonVariables: type: array maxItems: 20 items: type: string maxLength: 1024 description: >- The value for a link button's placeholder, when the template has one. headerMediaUrl: type: string format: uri maxLength: 2048 description: >- An `https://` link to the header's image, video or document, when the template has a media header. Leave it out to use the template's own. idempotencyKey: type: string description: >- Same as the `Idempotency-Key` header. The header wins when both are sent. example: template: name: order_update language: en variables: - Priya - '#10432' ConversationReplyForm: type: object title: Form required: - form properties: form: description: >- A published WhatsApp form of this workspace: its name as shown on the Forms page (`"Delivery address"`), its id (`form_…`), or `{ "name": "…" }` / `{ "id": "…" }` to say which outright. Only while the customer's 24-hour window is open. oneOf: - type: string maxLength: 200 title: Name or id - type: object title: By name required: - name properties: name: type: string maxLength: 200 description: The form's name. - type: object title: By id required: - id properties: id: type: string description: The form's id (`form_…`). idempotencyKey: type: string description: >- Same as the `Idempotency-Key` header. The header wins when both are sent. example: form: Delivery address 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. TooManyRequests: description: Over the per-minute limit. 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 240 requests a minute. Slow down and retry. 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.