Troubleshooting

Published on: January 10, 2026

Last updated: January 10, 2026

If rates are missing or you see USPS API errors, don’t panic – this is almost always configuration, credentials, or product data. The USPS OAuth platform is strict, and WooCommerce will refuse to calculate rates if weights, addresses, or zone rules are incomplete.

This page covers the most common failure modes: OAuth authentication errors, “no rates available,” sandbox vs production confusion, shipping zone misconfiguration, and how to capture logs we can actually use.

Rule of thumb: fix issues in this order – (1) WooCommerce basics, (2) plugin settings, (3) USPS credential status, (4) shipping zone rules, (5) logs.

Quick Checklist (Do These First)

  • WooCommerce store address is set (WooCommerce – Settings – General).
  • Origin ZIP code is configured in the plugin settings.
  • Products have weights (at least one shipping class must have weight).
  • Shipping zones include a zone matching the customer address.
  • The USPS method is added to that zone and enabled.
  • Sandbox Mode matches the credentials you’re using.

401 Unauthorized / Authentication Failures

Symptoms: 401 Unauthorized, invalid_client, token request fails, or the “Test Connection” button fails.

  1. Log into the USPS Business Customer Gateway and confirm your API credentials are Active (not Pending).
  2. Verify the correct USPS API access is enabled (the rate/pricing API you were approved for).
  3. Double-check that you copied the Client ID and Client Secret exactly (no trailing spaces).
  4. If you are using USPS test credentials, enable Sandbox Mode. If you are using live credentials, disable Sandbox Mode.

Common cause: Live credentials in Sandbox Mode (or sandbox credentials in production mode). This is the #1 OAuth mismatch.

No Rates Showing at Checkout

Symptoms: Customers see “No shipping options were found” or rates never appear.

  1. Check product weights: WooCommerce will not quote USPS rates without weight.
  2. Check dimensions: If your products don’t have dimensions, configure the plugin’s Default Dimensions.
  3. Check the address: Confirm the destination address is valid and complete (postal code matters).
  4. Check shipping zones: WooCommerce zones must match the customer country/state/ZIP range.
  5. Confirm services are enabled: If no domestic/international services are checked in the method settings, nothing can be returned.

Sandbox vs Production Confusion

Symptoms: Test Connection succeeds but checkout rates don’t, or live rates never show.

  • Sandbox Mode ON means the plugin talks to USPS test endpoints. Use this for setup verification and behavior testing.
  • Sandbox Mode OFF means the plugin talks to USPS production endpoints for real rates.
  • If you change modes, click Save Changes and run Test Connection again.

API Downtime / Timeouts

Shipping APIs occasionally hiccup. If USPS is unreachable, this plugin can show Fallback Rates so checkout stays functional.

  • If you rely on checkout stability, configure a Fallback Rate per shipping zone method.
  • If you see intermittent failures, enable logging and check whether the failures align with USPS response errors.

How to Enable Debug Logging

When you contact support, logs matter. Here’s the standard WordPress debug setup:

// wp-config.php
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);

After reproducing the issue, check:

  • /wp-content/debug.log

Tip: Reproduce once, then copy the relevant excerpt (don’t paste your entire log unless requested).

Before You Contact Support

Send this info so we can fix it in one pass instead of playing 20 questions:

  • WordPress version
  • WooCommerce version
  • PHP version
  • Plugin version
  • Sandbox Mode: on/off
  • Screenshot of your plugin settings (hide secrets)
  • Screenshot of the shipping zone method configuration
  • Relevant debug log excerpt (redact secrets)

Important: Never email your Client Secret. If we need to verify credential format, redact most of it.

Still Stuck?

If you’ve worked through the checklist and still can’t get rates, the fastest fix is usually a review of:

  • Shipping zone matching rules
  • Product weights/dimensions
  • Sandbox vs production mismatch
  • Credential approval status in USPS Gateway

Contact support with the info above and we’ll get you unstuck.

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