USPS Just Broke Your Magento Shipping. Here's the Fix.

If your Magento store still depends on the old USPS Web Tools integration, you should assume your shipping rates are either already broken or one change away from breaking. That sounds dramatic, but it is the practical reality we have been seeing. USPS has moved away from the old Web Tools model and toward REST API v3 with OAuth 2.0 authentication. Magento's legacy USPS integration was built for a different era. For merchants, the symptom is simple: rates stop showing up, return inconsistently, or fail under conditions you did not use to worry about. For Magento developers, the reason is also simple: the built-in carrier module is not designed for the current USPS authentication and request model. This article explains what changed, why core Magento falls over here, how to migrate cleanly, and what to watch for whether you choose an extension or a custom build. What changed: USPS Web Tools is not the same platform anymore Historically, Magento's USPS integration talked to Web Tools-style USPS endpoints: structured shipping requests, legacy authentication, and XML responses. That is not the model USPS wants merchants using now. The modern USPS stack is based on: REST API v3 endpoints OAuth 2.0 for authentication Different request and response payloads Different onboarding and credential management patterns That shift matters because it is not just a URL update. It changes authentication, token handling, and request structure. In practical terms, a migration now means: Getting the right USPS developer credentials Exchanging those credentials for OAuth access tokens Updating the carrier request layer to use REST payloads Mapping the new response format back into Magento shipping methods If you skip any of that and try to "patch" the old module with endpoint changes, you are going to waste time. Why Magento 2's built-in USPS module no longer works Magento's built-in USPS module was not architected around OAuth-backed REST API calls. It expects a legacy carrier contract