ShippingEasy partners with Stamps.com to provide USPS postage. You have 28 days from the date you created a USPS label to cancel it. Cancelling a USPS label automatically triggers a request for an refund.
The USPS must approve label cancellations, to ensure that the label was not actually used. It usually takes 21 days to approve a label cancellation. Then any refunded postage will be returned to your account.