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}}

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

When to use it

Reach for this scenario when billing must deliver a PDF invoice while a support conversation is still open on WhatsApp — the client already wrote first and the 24-hour session window is active. It fits billing follow-up inside helpdesk threads where attaching documents through approved templates would be slow or unnecessary for teams integrating 1MSG with ticket and invoicing backends.

Workflow

1. Trigger

   The helpdesk marks a ticket ready for invoicing while the session is still open.

   event · triggered

2. Capture event

   Your backend resolves the ticket number and invoice PDF location.

   phone: "+…"

3. Build & send

   sendFile sends application/pdf with filename invoice.pdf and a caption referencing the ticket.

   POST /send_file

4. Delivered

   The client receives the PDF in the same WhatsApp thread.

   delivered

Technical implementation

Prerequisites

1. 1MSG API Key · How to get API Key
2. WhatsApp Business account · How to Connect WABA
3. Open 24-hour session window · How the 24-hour window works
4. Customer opt-in · How to Manage Customers Consent
5. Webhook endpoint · How to Set Up Webhooks

Code examples

#!/usr/bin/env bash
set -euo pipefail

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



# === Test data ===
TEST_PHONE="___"                 # client phone in international format
MEDIA_URL="___"                         # local file path or HTTPS URL for sendFile body

PHONE_NORM="$(printf '%s' "$TEST_PHONE" | tr -cd '0-9')"
URL="${API_BASE_URL%/}/${CHANNEL_ID}/sendFile"

read -r -d '' PAYLOAD <<JSON || true
{
  "phone": "${PHONE_NORM}",
  "body": "https://www.w3.org/WAI/ER/tests/xhtml/testfiles/resources/pdf/dummy.pdf",
  "filename": "invoice.pdf"
}
JSON

RESPONSE="$(curl -s -w '\n%{http_code}' -X POST "$URL" \
  -H "Content-Type: application/json" \
  -H "Authorization: Bearer ${API_TOKEN}" \
  -d "$PAYLOAD")"

HTTP_CODE="$(printf '%s' "$RESPONSE" | tail -n1)"
BODY="$(printf '%s' "$RESPONSE" | sed '$d')"

case "$BODY" in
  *'"sent":true'*) ok=1 ;;
  *) ok=0 ;;
esac

if [ "$HTTP_CODE" -ge 200 ] && [ "$HTTP_CODE" -lt 300 ] && [ "$ok" -eq 1 ]; then
  echo "Message sent to client."
  echo "API response: $BODY"
else
  echo "Send failed. HTTP status: $HTTP_CODE" >&2
  echo "$BODY" >&2
  exit 1
fi

Response and delivery status

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 (looks like wamid.…) to correlate delivery callbacks.

{
  "sent": true,
  "id": "wamid.HBgLMzgwNjM5...",
  "message": "Message accepted for delivery"
}

Delivery itself arrives later, as a separate callback. Register a webhook (POST …/webhook) and 1MSG POSTs status updates to your HTTPS endpoint in a top-level hooks[] payload.

{
  "hooks": [
    {
      "id": "gBGGeSaGViBfAgnlzOSHEwK9O6F",
      "type": "message",
      "status": "sent",
      "timestamp": "1654864094",
      "recipient_id": "556123122026"
    }
  ]
}

If you would rather not receive callbacks, poll GET {base}/{channel}/hookInfo?messageId=<id> instead. In practice delivery often completes within seconds — but the API contract does not guarantee it, so never block a flow waiting on it.

Common errors

FAQ