WhatsApp Business API for session send — invoice pdf

Use case overview

This scenario sends a PDF document with sendFile during the 24-hour WhatsApp customer service window. Use it when billing must attach an invoice without starting a new template conversation.

Template example

Invoice for ticket {{1}}

sendFile works only when the 24-hour session window is open; the PDF URL in docs is a public test file.

Variables and purpose

• {{1}} — support ticket number shown in the PDF caption

Filled-in example

Invoice for ticket TKT-2048

When to use it

• billing follow-up

Business value

• Client message or reply keeps the WhatsApp session window open
• Backend resolves the ticket number and invoice PDF location
• sendFile delivers application/pdf with a personalised caption
• Client receives the invoice in the same support thread
• Delivery status is logged for the helpdesk or billing system

Workflow

1. The helpdesk marks a ticket ready for invoicing while the session is still open.
2. Your backend resolves the ticket number and invoice PDF location.
3. sendFile sends application/pdf with filename invoice.pdf and a caption referencing the ticket.
4. The client receives the PDF in the same WhatsApp thread.
5. Delivery progress is reported asynchronously — typically sent, then delivered (or failed/undelivered).
6. Your system receives status via webhook (hooks[]) or polls delivery status and handles failures if needed.

Technical implementation

Prerequisites

• An open WhatsApp session window (client wrote first or replied within 24 hours).
• 1MSG channel with sendFile access and a reachable PDF URL or local file.

Code examples

Node.js

#!/usr/bin/env node

// === Configuration (replace "___" placeholders) ===
const API_BASE_URL = "https://api.1msg.io"; // production 1MSG API base URL
const CHANNEL_ID = "___";                   // channel ID from 1MSG dashboard
const API_TOKEN = "___";                    // channel JWT token (Bearer)



// === Test data ===
const TEST_PHONE = "___";            // client phone in international format
const MEDIA_URL = "___";                    // local file path or HTTPS URL for sendFile body
const MEDIA_FILENAME = "invoice.pdf";
const TEST_CAPTION = "___";

function normalizePhone(phone) {
  return String(phone).replace(/\D/g, "");
}

async function sendSessionFileMessage({ phone, mediaUrl, caption }) {
  const url = `${API_BASE_URL}/${CHANNEL_ID}/sendFile`;
  const requestBody = {
    phone: normalizePhone(phone),
    body: mediaUrl,
    filename: MEDIA_FILENAME,
    caption: String(caption),
  };

  const res = await fetch(url, {
    method: "POST",
    headers: {
      "Content-Type": "application/json",
      Authorization: `Bearer ${API_TOKEN}`,
    },
    body: JSON.stringify(requestBody),
  });

  const raw = await res.text();
  let data;
  try {
    data = JSON.parse(raw);
  } catch {
    data = null;
  }

  if (!res.ok || !data || data.sent !== true) {
    console.error("Send failed. API response:");
    console.error(raw);
    process.exit(1);
  }

  console.log("Message sent to client.");
  console.log("API response:", raw);
  return data;
}

if (require.main === module) {
  sendSessionFileMessage({
    phone: TEST_PHONE,
    mediaUrl: MEDIA_URL,
    caption: TEST_CAPTION,
  }).catch((err) => {
    console.error("Execution failed:", err.message);
    process.exit(1);
  });
}

module.exports = { sendSessionFileMessage };

Immediate API response (synchronous)

• HTTP 2xx and JSON "sent": true mean 1MSG accepted the message for sending — not that it already reached the customer's phone.
• Save the `id` field from the response (value looks like wamid.…). Use it to correlate delivery callbacks or polling.
• The response may also include message and description — informational only.

Delivery status (asynchronous)

• Register a webhook (POST …/webhook) so 1MSG POSTs delivery updates to your HTTPS endpoint in a separate `hooks[]` payload (sent, delivered, read, or failed/undelivered when applicable).
• Optionally poll: GET {base}/{channel}/hookInfo?messageId=<id from sendTemplate>.
• In practice, delivery often completes within a few seconds — but that is not guaranteed by the API contract.

Common errors

• Session window closed (no client message within 24 hours)
• Invalid or non-normalized phone number
• Missing or invalid message body / media URL
• Delivery failure — check status webhook and retry policy

FAQ

• Do I need a template? No — this scenario uses a session message inside the 24-hour customer service window.
• When does the session window close? If the client has not written or replied within 24 hours, sendMessage will fail until a template reopens the chat.
• How do I check delivery? sent: true only confirms acceptance. Track delivery via webhook hooks[] or polling.
• What if the message is not delivered? Log the failed/undelivered hook, verify the session window, then retry or use a template.
• Can I connect this to my CRM or backend? Yes — trigger the API call from your inbound webhook or workflow engine.

CTA

Ready to use session send — invoice pdf? Connect your 1MSG channel and run the code examples above.

Related

• Knowledge base
• Creating a template
• Sending a template
• SDK