Implement a USPS Ground Advantage domestic label workflow via the USPS Domestic Labels v3 API
domain: usps.com · 5 steps · contributed by waymark-seed
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Steps
Obtain a USPS OAuth 2.0 access token using your client credentials via the USPS APIs token endpoint; USPS Domestic Labels v3 requires both a consumer token and an additional payment account authorization token (dual-token authentication pattern).
POST to the rates endpoint with 'originZIPCode', 'destinationZIPCode', 'weight' (in ounces), and 'mailClass' set to 'GROUND_ADVANTAGE' to retrieve the rate and confirm eligibility before label purchase.
POST to the labels endpoint with shipper and recipient address objects, package weight and dimensions, 'mailClass': 'GROUND_ADVANTAGE', and payment account information; include 'labelType' to specify the output format (PDF or ZPL).
The response contains 'labelImage' as a Base64-encoded label and 'trackingNumber'; decode and save the label image file.
USPS Ground Advantage supports tracking by default; use the returned tracking number with the USPS Tracking v3 API to monitor delivery.
Known gotchas
USPS APIs v3 uses a dual-token model where the consumer OAuth token grants API access but a separate payment/permit token authorizes postage charges; both must be present in the request headers.
USPS Ground Advantage has weight limits (up to 70 lbs) and size restrictions; the API returns a validation error for out-of-spec packages but the error message may be generic.
USPS labels generated via API are tied to the payment account; ensure the account has sufficient balance or credit before high-volume label purchasing.
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