Shippo automatically refunds unused USPS labels 30 days after creation, and this is reflected in the label data after 14 business days.

If a USPS label in your account is never used (scanned by the carrier), Shippo will automatically refund it 30 days after it's created. Your refund will be processed 14 business days after the shipment date on the label.

• How to refund a label – Shippo

You can also immediately refund by calling Shippo’s refunds API.

curl  https://api.goshippo.com/refunds/ \\
    -H "Authorization: ShippoToken " \\
    -d transaction="4503427478ea45a899e9b54abc4c5803"

• Refunds | Shippo

It’s nice and convenient that Shippo automatically handles refunds if you’re not in a hurry.

That’s all from the Gemba.