SIMPLE:
ACTIVATE ALL PACKAGES!!!!
GO TO AN ORDER YOU WANT TO SHIP AND GO TO PRINT A LABEL
WHEN YOU SELECT A USPS PACKAGE ALL THE PACKAGE OPTIONS ARE THERE (LIKE THE FLAT RATE BOXES AND ENVELOPES)
***I HAVE NO IDEA WHY THEY DON’T SHOW UP IN THE SHIPPING SETTINGS BUT THEY DO SHOW UP WHEN YOU ARE ACTUALLY AT THE POINT OF CREATING A LABEL.