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OAuth
3 posts in this collection.
3 reviewed guides
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OnboardingMarch 10, 2026
How to Get a USPS CRID and MID, and Link Them to the v3 API (2026)
A USPS CRID identifies the business; a MID identifies the mailer. Here is where to find them, connect the EPA, link COP claims, and activate v3 APIs.
16 min readTroubleshootingMarch 10, 2026
USPS v3 OAuth Troubleshooting: Every Error and How to Fix It
401, 403, and 429 from USPS v3, with the exact fix for each, including the Addresses API license that has gated address calls since August 1, 2026.
9 min readSDK ReferenceMarch 10, 2026
USPS v3 SDK for Python and Node.js: Endpoints, Credentials, and the OAuth You Do Not Have to Write
The usps-v3 SDKs for Python and Node.js at v1.0.4. Real method signatures, which calls need Payment Authorization, error classes, and token handling.
9 min read