Priority Mail Flat Rate packaging requires the corresponding Flat Rate labels
Flat Rate Labels for Flat Rate Packaging: If you want to use a Flat Rate Box or Envelope, you have to buy the specific corresponding postage in Pirate Ship.
For example, if you want to ship a Small Flat Rate Box, you must buy Small Flat Rate Box postage.
Selecting Your Flat Rate Packaging: To access this type of postage in Pirate Ship, click the "Type of Packaging" drop-down menu when creating your labels and select the type of Flat Rate Box or Envelope you're using.
This video shows you how that looks:
Enter Any Weight Up to 70 Pounds: When entering your weight, feel free to enter anything under 70 pounds 😉
Flat Rate postage isn't based on weight, so as long as your package weighs less than the 70-pound maximum limit, you'll be able to buy your label.
Order Free Priority Mail Flat Rate boxes: You can get free Flat Rate Boxes and Envelopes at your local Post Office, or you can order them online and have USPS ship them to you for free!