It sounds like, however you re calculating your shipping costs online, you re not doing it properly. You re obviously not paying enough to generate the preprinted label, if you have to pay more at the post office.Without knowing exactly what you re doing, we can t tell you what you re doing wrong. Are you weighing the items you re mailing? Are you weighing them correctly, after they re all wrapped and packaged for mailing?
Then you are screwing something up.If you can t figure out what you are doing wrong, don t pay online.