Generate prepaid return labels via carrier APIs for customer-initiated returns

Steps

1. Choose a multi-carrier label API (such as EasyPost) to avoid managing separate integrations for each carrier; authenticate with your API key in the Authorization header.
2. When a return is approved, create a return shipment object by POSTing to the shipments endpoint with the from_address set to the customer's address, the to_address set to your warehouse, and the parcel dimensions/weight.
3. Retrieve available rates from the rates array in the response; select the appropriate service (UPS, FedEx, or USPS) based on cost, speed, and whether the carrier supports pay-on-use electronic return labels.
4. Purchase the label by calling the buy endpoint with the selected rate ID; the response contains a postage_label.label_url from which you can download the label PDF or ZPL.
5. Deliver the label to the customer via email (as a link or attachment) or embed it in your returns portal for download; for electronic return labels (FedEx Email Return Label, UPS Electronic Return Label), the carrier charges only when the label is first scanned.
6. Store the tracking number against the RMA in your OMS; subscribe to tracking webhooks to monitor inbound return shipment status and trigger warehouse receiving workflows on delivery.