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Post-purchase upsell message via WhatsApp API

The scenario sends a personalised WhatsApp marketing template shortly after a completed purchase when a follow-up offer is relevant — a refill, companion product, or the next service in the cycle.

Use case overview

The scenario sends a personalised WhatsApp marketing template shortly after a completed purchase when a follow-up offer is relevant — a refill, companion product, or the next service in the cycle. The message includes the customer name, the product they bought, and details of the recommended offer. A static URL button opens the offer page.

Template example

Hello, {{1}}! Based on your recent purchase of "{{2}}", we have a follow-up offer for you: {{3}} Tap the button below to view the offer and order again.

View offer
  • {{1}}
    customer name
  • {{2}}
    product name from the previous purchase
  • {{3}}
    follow-up offer details (refill, companion product, next service)
  • “View offer”
    button — fixed in the Meta template
WhatsApp Business API for post-purchase follow-up offer

When to use it

Use this scenario when a customer recently completed a purchase and the business has a natural next buy — a refill, companion product, or the next step in a service cycle — to offer while the order is still fresh. It fits e-commerce and D2C brands suggesting replenishments days after delivery, subscription and consumables businesses prompting reorders before stock runs out, and agencies wiring post-order triggers from Shopify, WooCommerce, or CRM into WhatsApp cross-sell flows.

Repeat revenue while the purchase is fresh
The post-purchase trigger fires days after delivery or service completion, so the follow-up offer reaches the customer on WhatsApp while they still remember what they bought — not months later after they switched brands.
Offers tied to what they actually bought
Three body variables carry the customer name, the purchased product, and the recommended follow-up offer, so the message reads as a logical next step rather than a generic marketing blast.
Compliant outreach outside the 24-hour window
An approved MARKETING template delivers the cross-sell or refill offer even when no conversation is open, so the business does not depend on the client messaging first.
Less manual rep follow-up after orders
Order history resolves the phone and purchase fields, the template is built automatically, and delivery is logged — so reps do not retype order context or remember to send each follow-up offer by hand.
Cross-sell analytics on the same order record
Delivery result is written back to the e-commerce platform or CRM, so repeat-purchase campaigns report on the same order that triggered the follow-up offer.

Workflow

  1. Build & send

    The e-commerce platform or CRM fires a post-purchase follow-up trigger when the order is eligible.

    POST /sendTemplate

  2. Capture event

    The system resolves the recipient phone number and purchase fields from order history.

    phone: "+…"

  3. A personalised follow-up offer

    A personalised follow-up offer template is built with three body variables and a static URL button.

    POST /sendTemplate

  4. Delivered

    The client receives the WhatsApp marketing message with purchase context and the recommended offer.

    delivered

  5. Status tracked

    Delivery result is logged for repeat-purchase and cross-sell campaign analytics.

    status: "read"

WhatsApp Business API for post-purchase follow-up offer

Technical implementation

Prerequisites

  1. 1MSG API Key · How to get API Key
  2. WhatsApp Business account · How to Connect WABA
  3. WhatsApp Template · How to Approve WABA Template
  4. Customer opt-in · How to Manage Customers Consent

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)

TEMPLATE_NAME="___"                        # approved template name
TEMPLATE_NAMESPACE="___"                   # template namespace (required — send fails without it)
TEMPLATE_LANGUAGE="___"                    # template language code, e.g. "en"



# === Test data ===
TEST_PHONE="___"                 # client phone in international format
TEST_CUSTOMERNAME="___"         # {{1}} customer name
TEST_PRODUCTNAME="___"         # {{2}} product name
TEST_ADDITIONALINFO="___"         # {{3}} additional info

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

for pair in "CHANNEL_ID=$CHANNEL_ID" "API_TOKEN=$API_TOKEN" \
            "TEMPLATE_NAME=$TEMPLATE_NAME" "TEMPLATE_NAMESPACE=$TEMPLATE_NAMESPACE" \
            "TEMPLATE_LANGUAGE=$TEMPLATE_LANGUAGE" "TEST_PHONE=$TEST_PHONE" \
            "TEST_CUSTOMERNAME=$TEST_CUSTOMERNAME" \
            "TEST_PRODUCTNAME=$TEST_PRODUCTNAME" \
            "TEST_ADDITIONALINFO=$TEST_ADDITIONALINFO"; do
    val="${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}/sendTemplate"

# params carries body ONLY. Button text is fixed in the Meta template — no button param.

# {{1}} customer name → ${TEST_CUSTOMERNAME}
# {{2}} product name → ${TEST_PRODUCTNAME}
# {{3}} additional info → ${TEST_ADDITIONALINFO}
read -r -d '' PAYLOAD <<JSON || true
{
  "phone": "${PHONE_NORM}",
  "template": "${TEMPLATE_NAME}",
  "namespace": "${TEMPLATE_NAMESPACE}",
  "language": { "policy": "deterministic", "code": "${TEMPLATE_LANGUAGE}" },
  "params": [
    {
      "type": "body",
      "parameters": [
        { "type": "text", "text": "${TEST_CUSTOMERNAME}" },
        { "type": "text", "text": "${TEST_PRODUCTNAME}" },
        { "type": "text", "text": "${TEST_ADDITIONALINFO}" }
      ]
    }

  ]
}
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,
  "message": "Sent to [email protected]",
  "description": "Message has been sent to the provider",
  "id": "wamid.HBgLMzgwNjM5..."
}
  • sent

    Accepted for sending — not yet on the customer's phone

  • id

    Store it; delivery callbacks and hookInfo are keyed on this

Delivery statuses and webhooks →

Common errors

StatusAPI responseCauseFix
200Message was not sent: template is not definednamespace, template or language is missing from the request body.Send all three. Take namespace and the exact template name from GET /templates; language is an object: {"policy": "deterministic", "code": "en"}.
200template name (…) does not exist in <language>The template is approved in a different language than the one requested.Use the exact language code the template was approved in (for example es_MX is not the same as es). Check it in GET /templates.
200Message was not sent: provide chatId, phone, bsuid, or usernameNo recipient the channel could resolve.Pass exactly one recipient: phone (country code plus number, digits only), chatId (for example [email protected]) or bsuid.

All error codes →

Common questions

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