Pirate Ship only offers labels for USPS® parcel shipping services. If you're just trying to mail a letter, you're best off buying some cool stamps at the Post Office 😉
Why Pirate Ship does not offer stamps or postage for mailing letters
Pirate Ship is built for eCommerce shipping, so we do not offer any USPS® mail services for domestic or international, as those services are meant for letters and documents, not merchandise.
Some of the mailing services that Pirate Ship does not offer include the following:
First-Class Mail
Metered Mail
Marketing Mail
Bound Printed Matter
Forever stamps
Certified Mail
First Class Mail International Large Envelope
Flat services
These mailing services above don't come with tracking (while the labels have a number that LOOKS like a tracking number, it isn't one). Every shipping service, on the other hand, includes tracking.
Since mailing services like First Class Mail International Large Envelope / Flat service are not intended for merchandise, USPS® will reject and return your packages if you try to use these mailing services to send anything other than documents.
You should be using USPS Ground Advantage® or First Class Package International® instead.