OnShip multi-carrier shipping software can process USPS, UPS and FedEx Return labels.
What are return labels? The ultimate guide for sellers
Return Shipping Labels
Online Postage Services Part 1: Endicia Innovates
Simplify Returns with Pre-Paid Return Shipping Labels - ReturnGO
Purchase this product to receive a prepaid shipping label from us for your return. Note this is a manual process, and will not be handled instantly.
Return Shipping Label - USA
Prepaid Return Labels – ShippingEasy
ReturnZap - Providing Prepaid Return Labels to Customers
Can I use a different service for USPS return labels?
MCF returns: Pre-paid return labels