Register an application on developers.usps.com and obtain OAuth 2.0 client credentials; the v3 platform requires token-based authentication for all label and returns API calls.
Identify the appropriate returns service: USPS returns labels support Priority Mail Return, Ground Return, and Priority Mail Express Return service types; select based on merchant SLA and cost requirements.
POST to the USPS Returns Label API endpoint with shipper account, return-to address, return-from address (customer), service type, weight estimate, and label format (PDF, ZPL, or other supported format).
The API response includes the label image, an Intelligent Mail Package Barcode (IMpb), and a USPS tracking number — store the tracking number against the return merchandise authorization (RMA) record.
Deliver the label to the customer via email link or embed it in the returns portal; the customer drops the package at any USPS location or schedules a carrier pickup.
Monitor the return tracking number via the USPS Tracking API v3 to detect when the package is in transit and when it arrives at your returns processing facility.
Known gotchas
The legacy USPS Web Tools XML API for returns labels is on a deprecation path; build only against the v3 REST API on developers.usps.com to avoid a forced migration.
USPS introduced an API Access Control initiative (launching in phases through 2026) that adds additional credential scoping — provision the correct scopes for returns label generation at onboarding, as missing scopes result in authorization errors rather than clear error messages.
Returns labels generated without a weight estimate may result in postage-due charges applied to the return package; always supply a reasonable weight estimate even if the exact contents are unknown.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp