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Polar Integration

Connect your Polar account to Windback via the custom webhook endpoint to detect subscription cancellations and changes.
Polar does not have a native Windback integration. This guide uses a lightweight Node.js relay function that receives Polar webhooks and forwards them to Windback’s custom webhook endpoint.

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Webhook URL

Your Windback custom webhook URL is: 
https://api.windbackai.com/api/v1/webhooks/custom/<your_public_key>
Your public key starts with pub_ and is found in Settings > API Keys.

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Setup

1

Deploy the Relay Function

Deploy the Node.js relay function below to your server or a serverless platform (Vercel, AWS Lambda, etc.). This function receives Polar webhooks, maps the payload, and forwards it to Windback.
2

Add the Webhook in Polar

  1. Go to Polar Dashboard > Settings > Webhooks
  2. Click Add Endpoint
  3. Paste the URL of your deployed relay function
  4. Select the events listed below
  5. Save the webhook
Polar provides a webhook secret for signature verification. Store it securely and validate incoming requests.
3

Select Webhook Events

Enable the following events in Polar:
Polar EventWindback Event TypeDescription
subscription.canceledcancellationCustomer canceled their subscription
subscription.updatedConditionalCheck the status field — forward as payment_failed if status is past_due, or payment_recovered if status returns to active
4

Verify the Connection

  1. Create a test subscription in Polar’s sandbox environment
  2. Cancel the subscription to trigger a subscription.canceled event
  3. Check your Windback dashboard for the new churn event

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Data Mapping

The relay function maps Polar fields to Windback’s custom webhook format:
Polar FieldWindback FieldNotes
data.user.emailcustomer_emailSubscriber email address
data.user.usernamecustomer_namePolar username
data.product.nameplan_nameProduct name
data.amountmrrAmount in cents
data.currencycurrencyISO 4217 code
data.created_attenure_daysCalculated from subscription start

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Relay Function

const express = require("express");
const app = express();
app.use(express.json());

const WINDBACK_URL =
  "https://api.windbackai.com/api/v1/webhooks/custom/pub_your_key";

function mapPolarEvent(event, data) {
  if (event === "subscription.canceled") {
    return "cancellation";
  }
  if (event === "subscription.updated") {
    if (data.status === "past_due") return "payment_failed";
    if (data.status === "active") return "payment_recovered";
  }
  return null;
}

app.post("/polar-webhook", async (req, res) => {
  const { event, data } = req.body;

  const windbackEventType = mapPolarEvent(event, data);
  if (!windbackEventType) {
    return res.status(200).json({ status: "skipped" });
  }

  const user = data.user || {};
  const product = data.product || {};

  const tenureDays = data.created_at
    ? Math.floor(
        (Date.now() - new Date(data.created_at).getTime()) / (1000 * 86400)
      )
    : undefined;

  const payload = {
    customer_email: user.email,
    customer_name: user.username || undefined,
    event_type: windbackEventType,
    mrr: data.amount || undefined,
    currency: data.currency?.toLowerCase() || "usd",
    provider: "polar",
    plan_name: product.name || undefined,
    tenure_days: tenureDays,
  };

  try {
    await fetch(WINDBACK_URL, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify(payload),
    });
  } catch (err) {
    console.error("Failed to forward to Windback:", err);
  }

  res.status(200).json({ status: "ok" });
});

app.listen(3000, () => console.log("Polar relay listening on port 3000"));
Replace pub_your_key with your actual Windback public key. Never commit your real key to version control.

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Webhook Resilience

Windback’s custom webhook endpoint always returns HTTP 200 regardless of internal processing status. Your relay function should also always return 200 to Polar to prevent webhook retries.
Polar signs webhook payloads using a shared secret. We recommend verifying the signature in your relay function before forwarding to Windback. See Polar’s webhook documentation for details.