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Connect WhatsApp → your number → Connect External Agent/CRM. You already have a CRM or an agent platform of your own — your own prompts, your own voice and chat stack — and you want it on WhatsApp without building a WhatsApp integration. Switch on Connect External Agent/CRM for a number and ThinnestAI stops answering it. Every message a customer sends is passed to your external agent, and its replies go back to the customer through us. What stays with ThinnestAI: the connected number, the shared inbox where your team sees every thread and can take one over, templates, forms, opt-outs (“STOP”) and Meta’s 24-hour rule.

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How a message travels

  1. A customer writes to your WhatsApp number.
  2. We store it in the inbox and post it to your platform’s address as message.received.
  3. Your agent decides what to say.
  4. Your platform calls POST /api/v1/conversations/{conversationId}/reply.
  5. We send it on WhatsApp and add it to the thread as the agent’s reply.
Your agent can take as long as it needs — nothing waits on it. A reply sent after the customer’s 24-hour window has closed must be an approved template.

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Only want the WhatsApp API?

If nothing of ours should answer — your own software does all of it — pick WhatsApp API when you sign up, under What will you use it for? You land on WhatsApp instead of Agents, and every number you connect starts with Connect External Agent/CRM already on. There is no agent to set up and no toggle to find; follow the steps under the number. Changed your mind — want voice or our AI agent too? Pick another use case from the dropdown in the top bar; your connected numbers keep answering through your software until you change them. You pay Meta’s fee to Meta and 10% of it to us, per message. Nothing for AI — no agent of ours runs. On the Free plan, your first 200 messages (one time) carry none of our charges; after that, switch to Pay as you go (no monthly fee) to keep sending.

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Set it up

1

Connect your WhatsApp number

On WhatsApp, connect your own WhatsApp Business Account — a new one or one you already have.
2

Switch on Connect External Agent/CRM

Under the number, switch on Connect External Agent/CRM. Our agent picker moves to Not assigned and locks — nothing of ours answers this number. The number then shows these same steps. Only admins can change it; switching it off hands the number back, and you choose one of our agents again.
3

Create an API key

Settings → API keys. Send it on every call as Authorization: Bearer ta_live_…. See authentication.
4

Give us your external agent's address

Under the number, paste the HTTPS address customer messages should be posted to and press Save. The signing secret is shown once — keep it. Saving again mints a new one.
5

Reply

Call POST /api/v1/conversations/{id}/reply with the conversationId from the event.
Until you save an address, customer messages go nowhere and nobody answers them. The WhatsApp page shows a red warning under the number when that is the case, and again if your platform starts refusing deliveries.

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What your webhook receives

  • media — when the customer sent a photo, voice note, video or document: { "kind": "image" | "audio" | "video" | "file", "mimeType", "filename" }. The file itself is not in the event — read the conversation’s messages for a download link.
  • form — when the customer submitted a WhatsApp form: { "answers": { "field": "value" } }.
  • text — the message, or a media message’s caption.
  • messageId — the same id the messages API returns, so you can tell a message you already handled from a new one.
Every delivery carries x-thinnest-signature: sha256=…, an HMAC-SHA256 of the raw body under your signing secret. Check it before trusting the body. Every message is sent, not just the last one in a burst. If a customer sends three messages quickly, your platform gets three events.

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What your agent can send

One kind per call. The full reference, with every refusal, is on Reply to a conversation.

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When a person takes over

If a teammate takes a conversation over in the inbox, your agent’s replies to it are refused, and its new messages are not sent to your webhook, until the conversation is handed back. That way the customer never has two voices answering at once. The teammate’s exchange can be read through the conversations API. “STOP” and other opt-outs are handled before anything reaches you. The customer is unsubscribed from marketing whatever your agent does.

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Pricing

Meta bills your WhatsApp Business Account directly for its fee on each message, at Meta’s rates. ThinnestAI charges 10% of Meta’s rate per message, from your wallet — pay as you go, with no monthly subscription. A message Meta does not charge for costs nothing from us either. Replies your teammates send from the inbox or a connected helpdesk on these numbers are charged the same way. There is no AI usage to pay for on these numbers, because your agent does the answering.

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If your endpoint misses a message

Each message is sent once. One your endpoint does not accept is not retried, and the WhatsApp page shows the last failure under the number. Nothing is lost: read back what you missed with the conversations API.

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Not available yet

  • No typing indicator or read receipts from your agent.
  • WhatsApp only. Website chat, Telegram and voice are answered by ThinnestAI agents.