Can’t Create Label for APO Address

Description

Paypal accepts the APO address, not a problem. I create the required customs form, not a problem. But try to print the Priority Mail label and I get « Unable to print the requested label at this time. The following error occurred. The total weight of items listed on the customs form doesn’t match the shipment weight. Please check the information and try again. »
Problem is, I’m shipping Priority Mail Flat Rate Medium box. So why do I get an error that the customs form total weight doesn’t match the FLAT RATE box weight, when there is no place on the shipping screen to even enter a weight (there is no weight entry field when using flat rate packages)? Arrgghh!!!