Building a WhatsApp AI Sales Agent That Takes Payment

// WhatsApp Business Cloud API webhook handler
app.post('/whatsapp/webhook', async (req, res) => {
  res.sendStatus(200); // acknowledge immediately

  var message = req.body.entry?.[0]?.changes?.[0]?.value?.messages?.[0];
  if (!message || message.type !== 'text') return;

  var from = message.from;      // customer WhatsApp number
  var text = message.text.body;

  // Load conversation history from DB (keyed by phone number)
  var history = await db.whatsappSessions.get(from) || [];
  history.push({ role: 'user', content: text });

  var response = await runSalesAgent(history, from);

  // Send reply via WhatsApp Cloud API
  await sendWhatsAppMessage(from, response.reply);

  // Save updated history
  history.push({ role: 'assistant', content: response.reply });
  await db.whatsappSessions.set(from, history);
});

var salesTools = [
  {
    name: 'get_product_catalog',
    description: 'Get the list of available products with prices.',
    input_schema: { type: 'object', properties: {} },
  },
  {
    name: 'create_payment_link',
    description: 'Create a Paystack payment link for a confirmed order.',
    input_schema: {
      type: 'object',
      properties: {
        product_id: { type: 'string' },
        customer_name: { type: 'string' },
        customer_email: { type: 'string' },
      },
      required: ['product_id', 'customer_name', 'customer_email'],
    },
  },
];

async function runSalesAgent(history, customerPhone) {
  var response = await anthropic.messages.create({
    model: 'claude-opus-4-6',
    max_tokens: 512,
    tools: salesTools,
    messages: history,
    system: 'You are a sales agent for McTaba. Help customers find the right product and guide them to payment. Always confirm the order before creating a payment link. Collect customer name and email before creating a link.',
  });

  for (var block of response.content) {
    if (block.type === 'tool_use') {
      if (block.name === 'get_product_catalog') {
        var catalog = await db.products.getAll(); // your product DB
        // Feed result back and continue
        return runSalesAgent([
          ...history,
          { role: 'assistant', content: response.content },
          { role: 'user', content: [{ type: 'tool_result', tool_use_id: block.id, content: JSON.stringify(catalog) }] },
        ], customerPhone);
      }

      if (block.name === 'create_payment_link') {
        var product = await db.products.getById(block.input.product_id);
        var linkRes = await fetch('https://api.paystack.co/paymentrequest', {
          method: 'POST',
          headers: { Authorization: 'Bearer ' + process.env.PAYSTACK_SECRET_KEY, 'Content-Type': 'application/json' },
          body: JSON.stringify({
            description: product.name,
            amount: product.amount_kobo,
            currency: 'NGN',
            customer: { email: block.input.customer_email, first_name: block.input.customer_name },
          }),
        });
        var link = (await linkRes.json()).data;
        return { reply: 'Here is your payment link for ' + product.name + ': https://paystack.com/pay/' + link.offline_reference + '

It expires in 24 hours. Reply DONE once you have paid.' };
      }
    }
  }

  return { reply: response.content.find(b => b.type === 'text')?.text };
}

See agentic safety rails if you extend this agent to handle payouts or refunds.

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