Pirate Ship only offers postage 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 😉
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 don't include tracking (although the labels do include a number that LOOKS like a tracking number, it isn't one), while every shipping service 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 services to mail anything other than documents. You should be using USPS Ground Advantage® or First Class Package International® instead.