FAQ
Why did USPS rates stop working in my store?
Section titled “Why did USPS rates stop working in my store?”USPS retired the Web Tools API on 25 January 2026. CS-Cart 4.17 and 4.18 ship a USPS module that still calls Web Tools, so it returns no prices. This add-on uses the new USPS APIs (OAuth 2.0). Switch your USPS shipping methods to the carrier USPS (new APIs).
I am on CS-Cart 4.21. Do I still need it?
Section titled “I am on CS-Cart 4.21. Do I still need it?”CS-Cart 4.21 includes a USPS module for rates on the new APIs. This add-on adds what it does not have: labels, void and refund, tracking with delivered status, address validation, flat rate boxes per method, box presets, markup, free shipping threshold, fallback rate and per-vendor accounts. Both can run side by side.
What does USPS charge?
Section titled “What does USPS charge?”The developer app is free. You pay USPS postage for the labels you buy, from your own Enterprise Payment Account. The add-on adds no per-label fee.
Do I need a USPS business account?
Section titled “Do I need a USPS business account?”For rates, address validation and tracking: only the free developer app. For labels: a CRID, a Mailer ID and an Enterprise Payment Account, and USPS must enable the Labels and Payments APIs for your app (see Installation).
Can I test without buying postage?
Section titled “Can I test without buying postage?”Yes. Switch USPS environment to Test: calls go to the USPS Testing Environment for Mailers, where labels are not charged and cannot be mailed. USPS decides which apps get test access.
Which currency are prices in?
Section titled “Which currency are prices in?”USPS prices are in US dollars. Your store needs a USD currency; CS-Cart converts the price into the currency the customer sees. Markup and free shipping thresholds on the Configure tab are in USD.
Why is a method missing at checkout?
Section titled “Why is a method missing at checkout?”USPS did not return that service for the package (for example, over 70 lb, Media Mail for non-eligible items, or an invalid ZIP Code), the USPS account is not set up, or USPS could not be reached. Set a Fallback rate to keep the method visible, and see USPS labels → API log for the reason.
Can vendors print their own labels?
Section titled “Can vendors print their own labels?”Yes, in Vendors label mode: each vendor connects its own USPS account in the vendor panel and pays its own postage. In Marketplace owner mode the marketplace buys all labels and vendors see the tracking.
Is the customer notified when I buy a label?
Section titled “Is the customer notified when I buy a label?”The add-on creates the shipment without a notification. Send the shipment e-mail from the order as usual if you want the customer to get the tracking link right away; the customer account always shows USPS tracking.
Where are the labels stored?
Section titled “Where are the labels stored?”In the store database with the order, so they can be printed again at any time. Uninstalling removes them.
Is this an official USPS product?
Section titled “Is this an official USPS product?”No. USPS is a trademark of the United States Postal Service. This add-on is not affiliated with or endorsed by USPS; it uses the public USPS APIs with your own credentials.
Still stuck?
Section titled “Still stuck?”Work through the troubleshooting guide, then contact support with your CS-Cart version, edition, PHP version and the add-on version (1.0.0).