There is an option with Shippo to only process a charge once the prepaid label has been scanned. This is the so-called scan-based return label.
Shippo supports this currently for USPS, FedEx, and UPS. You can enable this in your Rich Returns dashboard when configuring your Shippo connection and enabling "Scan Based Labels"
For more information on return labels from Shippo and helpful insights, you can check this link here: https://goshippo.com/shipping/return-shipping-labels/.
Note that EasyPost does support a variety of return labels as well which are typically scan-based.
ShipStation does not support return labels through their API however.