Generate USPS returns labels via the USPS APIs v3 platform

Steps

1. 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.
2. 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.
3. 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).
4. 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.
5. 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.
6. 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.