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This guide explains how to use ngrok to receive Modern Treasury webhooks on your localhost app. By integrating ngrok with Modern Treasury, you can:
  • Develop and test Modern Treasury webhooks locally without deploying to a public environment or setting up HTTPS.
  • Inspect and troubleshoot requests from Modern Treasury in real time via the inspection UI and API.
  • Modify and replay Modern Treasury webhook requests with a single click instead of reproducing events manually in your Modern Treasury account.
  • Secure your app with Modern Treasury webhook validation provided by ngrok. Invalid requests are blocked by ngrok before reaching your app.

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What you’ll need

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1. Start your app

For this tutorial, you can use the sample Node.js app on GitHub. To install the sample, run the following in a terminal: 
git clone https://github.com/ngrok/ngrok-webhook-nodejs-sample.git
cd ngrok-webhook-nodejs-sample
npm install
Then start the app: 
npm start
The app runs on port 3000 by default. You can confirm it’s running by visiting http://localhost:3000. The app logs request headers and body in the terminal and shows a message in the browser.

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2. Expose your app with ngrok

Once your app is running locally, you’re ready to put it online securely using ngrok.
The ngrok agent uses your authtoken to authenticate when you start a tunnel.
  • Start ngrok: 
    ngrok http 3000
  • Copy the URL ngrok displays. Your app is now exposed at that URL for use with Modern Treasury.

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3. Configure Modern Treasury to send webhooks

Modern Treasury can send webhook requests to your app when events occur in your account. To register for those events:
  • Sign in to the Modern Treasury site.
  • Click View Sandbox to switch to Sandbox mode if you want to use example accounts.
If you have an active Modern Treasury account, you can skip switching to Sandbox.
  • Click Developers, the Webhooks tab, and then Create New Webhook Endpoint.
  • On New webhook, enter your ngrok URL in Webhook URL (for example, https://1a2b-3c4d-5e6f-7g8h-9i0j.ngrok.app).
  • Ensure Receive all events is selected for Events to send and click Save.

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Run webhooks with Modern Treasury and ngrok

Modern Treasury sends different request body contents depending on the event. To trigger new calls from Modern Treasury to your app:
  • On the Modern Treasury site, switch to Sandbox if needed.
  • Click Payments and Payments Overview.
  • Click Create New and Payment Order.
  • On Create Payment Order, click Pay, select a revenue account in From, a counterparty in To, ACH as Payment Method, enter an amount (for example, $10.00), and click Create Payment Order.
Confirm your localhost app receives event notifications as the payment updates and logs both headers and body in the terminal. You can verify events in Modern Treasury under Developers, Events tab.

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Inspecting requests

ngrok’s Traffic Inspector captures all requests made through your ngrok endpoint to your localhost app. Select any request to view detailed information about both the request and response.
To avoid exposing secrets, accounts only collect traffic metadata by default. You must enable full capture in the Observability section of your account settings to capture complete request and response data.
Use the traffic inspector to:
  • Validate webhook payloads and response data
  • Debug request headers, methods, and status codes
  • Troubleshoot integration issues without adding logging to your app

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Replaying requests

Test your webhook handling code without triggering new events from your service using the Traffic Inspector’s replay feature:
  1. Send a test webhook from your service to generate traffic in your Traffic Inspector.
  2. Select the request you want to replay in the traffic inspector.
  3. Choose your replay option:
    • Click Replay to send the exact same request again
    • Select Replay with modifications to edit the request before sending
  4. (Optional) Modify the request: Edit any part of the original request, such as changing field values in the request body.
  5. Send the request by clicking Replay.
Your local application will receive the replayed request and log the data to the terminal.

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Secure webhook requests

ngrok can verify that incoming requests are from your Modern Treasury webhook so only that traffic reaches your app.
Webhook verification is limited to 500 validations per month on free accounts. If you need more, you can upgrade to Hobbyist or Pay-as-you-go. See TPU Pricing for details.
To add verification:
  • In Modern Treasury, go to Developers, Webhooks tab, and click your webhook URL.
  • On the webhook page, copy the Webhook Key value.
  • Create a Traffic Policy file named modern_treasury_policy.yml. Replace {your webhook key} with the value you copied: 
    on_http_request:
  - actions:
      - type: verify-webhook
        config:
          provider: modern_treasury
          secret: "{your webhook key}"
  • Restart ngrok with the policy file: 
    ngrok http 3000 --traffic-policy-file modern_treasury_policy.yml
  • Create a new payment order in Modern Treasury to trigger the webhook.
Your app should receive the request and log it in the terminal.