Cahoot has made it very easy to void Shipping Labels.
Simply navigate to the Sales Order page and click the Void Label button in the Shipments section at the bottom of the page. After confirming your request, the Void Label button becomes a Create Shipping Label button so any errors can be corrected on the new label.
Orders that will not require creation of a new shipping label should be Excluded so Cahoot doesn't expect that a shipping label is missing for that order. Simply use the Exclude Order button that becomes visible at the top of the Sales Order page after the shipping label has been voided:
Note: Voiding Labels will automatically initiate a refund. However, it will take several weeks for the refund to process for all USPS labels AND for UPS or FedEx labels generated through Amazon Buy Shipping using Amazon's pass-through rates.