If you want to use a Flat Rate Box or Envelope you have to buy specific postage. For example, if you want to ship a Small Flat Rate Box, you have to buy Small Flat Rate Box postage.

To access this type of postage in Pirate Ship, just click the Type of Packaging dropdown when you're creating your labels and select the type of Flat Rate Box or Envelope that you're using: 

A gif showing how to create a label for a shipment using Flat Rate packaging. First, you'll click 'Create a Single Label' at the top center of the Ship Page, and on the following page, you'll scroll down to a section that says 'Type of Packaging.' There's a drop down menu below that header, and if you scroll down the options in that menu, you will see the different Priority Mail Flat Rate packaging options. Once you select a Flat Rate packaging, you'll enter the weight in pounds and ounces below.

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! Just go to https://store.usps.com.

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