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.

WhatsApp Business API for session reply — incoming client request

This scenario sends a free-text WhatsApp message with sendMessage inside the 24-hour customer service window after the client wrote first about a product or service.

Try the demo View code example

Use case overview

This scenario sends a free-text WhatsApp message with sendMessage inside the 24-hour customer service window after the client wrote first about a product or service.

Template example

Hello, {{1}}! We received your request about «{{2}}». {{3}} is reviewing it and will reply shortly.

{{1}}
client name
{{2}}
request topic or product area
{{3}}
assigned sales manager name

WhatsApp Business API for session reply — incoming client request

When to use it

Use this scenario when a prospect writes first on WhatsApp asking about a product or service and you need to acknowledge the request before a sales manager replies with details. It fits sales inbound flows where the client already opened the 24-hour session window and leaving them without a reply risks losing the lead.

Fewer leads left waiting

An inbound webhook triggers sendMessage as soon as the client message arrives, so the prospect gets acknowledgment in the same session before a manager opens the thread.

No template cold-start friction

sendMessage works inside the open 24-hour customer service window, so you skip template approval and the extra cost of reopening a dialog the client already started.

Request topic stays in the chat

Three body variables carry the client name, the request topic your backend extracted from CRM, and the assigned manager, so the acknowledgment is searchable in WhatsApp instead of a generic receipt.

Clear handoff to sales

The message names the assigned manager and sets expectation for a detailed reply in the same session, so the client knows who is handling the request while the manager prepares the answer.

Workflow

Status tracked
An inbound client message arrives via webhook.
status: "read"
Capture event
Your backend maps the chat to a lead and extracts the request topic.
POST /sendMessage
Build & send
A session text message acknowledges the request and names the manager.
POST /sendMessage
Delivered
The manager continues the dialog with a detailed answer in the same session.
delivered

Technical implementation

Prerequisites

1MSG API Key · How to get API Key
WhatsApp Business account · How to Connect WABA
Open 24-hour session window · How the 24-hour window works
Customer opt-in · How to Manage Customers Consent
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 · requires open 24-hour session window
TEST_CUSTOMERNAME="___"         # {{1}} customer name
TEST_TOPIC="___"         # {{2}} topic or subject
TEST_MANAGERNAME="___"         # {{3}} manager name

PHONE_NORM="$(printf '%s' "$TEST_PHONE" | tr -cd '0-9')"

for pair in "CHANNEL_ID=$CHANNEL_ID" "API_TOKEN=$API_TOKEN" "TEST_PHONE=$TEST_PHONE" \
            "TEST_CUSTOMERNAME=$TEST_CUSTOMERNAME" \
            "TEST_TOPIC=$TEST_TOPIC" \
            "TEST_MANAGERNAME=$TEST_MANAGERNAME"; do
  val="${pair#*=}"
  if [ -z "$val" ] || [ "$val" = "___" ]; then
    echo "Missing configuration value: ${pair%%=*}" >&2
    exit 1
  fi
done

if [ -z "$PHONE_NORM" ]; then
  echo "Error: phone number has no digits after normalization" >&2
  exit 1
fi

URL="${API_BASE_URL%/}/${CHANNEL_ID}/sendMessage"

read -r -d '' PAYLOAD <<JSON || true
{
  "phone": "${PHONE_NORM}",
  "body": "Hello, Alexey! We received your request about «CRM for a sales team». Manager Anna is reviewing it and will reply shortly."
}
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.

200 OKResponse

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

sent
Accepted for sending — not yet on the customer's phone
id
Store it; delivery callbacks and hookInfo are keyed on this

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.

200 OKDelivery status webhook — payload you receive

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

status
sent, delivered, read — or a failure status when applicable
id
Correlates the callback with the id returned by the send call
timestamp
Unix seconds, as a string

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

Status	Response	Cause
200	Message was not sent: empty body	No body in the request.
200	Message was not sent: provide chatId, phone, bsuid, or username	No recipient the channel could resolve.
200	wrong file	The media could not be fetched or uploaded — not a reachable URL, not valid base64.
403	access denied	The token is wrong, or belongs to a different channel than the URL.
200	Message was not sent: filename	sendFile called without a filename, so the media has no extension to send.