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USPS – How to fix the “Unknown Exception” error in WooCommerce?

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If you are using the USPS Live Rates PRO plugin for WooCommerce and encounter the error message:

USPS Live Rates: Unknown Exception

This guide will help you understand what it means and how to resolve it.

What does “Unknown Exception” mean?

The error comes directly from USPS API. It indicates that the client application credentials used for connecting your store with USPS are either:

  • missing,
  • invalid,
  • inactive,
  • not yet approved for access by USPS.

In other words, WooCommerce is trying to connect to USPS, but USPS rejects the request. This is not a plugin bug – it’s an external issue on the USPS side.

Step 1: Double-check your USPS credentials

Make sure you are using the correct Consumer Key and Consumer Secret from your USPS developer account.

  • Go to your USPS Developer Portal: https://developer.usps.com
  • Navigate to My Apps and verify that your application is correctly created.
  • Copy the Consumer Key and Consumer Secret exactly as shown (avoid extra spaces or hidden characters).

Tip: If your credentials do not work in our plugin, they also won’t work in any other USPS integration, because all plugins communicate with the same USPS API.

Step 2: Authorize your application

USPS requires that your app is explicitly authorized before it can access protected resources like rates, payment accounts, permits, CRIDs, and MIDs.

To authorize:

  1. Go to the USPS OAuth authorization page:
    https://cop.usps.com/navigator?wf=apisonboarding&callback=https://developers.usps.com
  2. Enter your Consumer Key.
  3. Follow the steps to approve your application for API access.

Step 3: Contact USPS Support if needed

In some cases, even after creating the app, USPS may need to manually activate or approve your account.

If the error persists, reach out directly to USPS Web Tools Support:

Explain that you are receiving an “Unknown Exception” error when trying to fetch rates with your Consumer Key and Secret, and ask them to confirm that your account is fully activated.

Additional Resources

Once your USPS account is properly authorized and active, the error will disappear and live rates will display correctly at checkout.

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