After you've enabled USPS rates by following the steps under Live Rates > Add Carrier on the Shipping page, you'll need to contact USPS to request label printing access for your account. Give USPS the following information, either via email (email@example.com) or by phone (1-800-344-7779):
I am using third-party ecommerce software called Volusion. My USPS username is XXXXXX. Please give my account access to the USPS ExpressMailLabel API. I will not be altering the labels. I will also need access to the USPS Delivery Confirmation V4.
Be sure to replace "XXXXXX" with your username, and include "Web Tools API Access" in the email's subject line.
In some cases, USPS may tell you that you already have access to the production server. While this is necessary to receive live rates, it is only part of the access needed to print shipping labels. Until USPS provides your account with access to the label printing functions of their API, you will not be able to print labels.
In other cases, USPS may refer you back to Volusion, advising that:
There is a line of code that refers to "shippingapitest.dll". You'll need to remove the word "test".
We have already performed that step. This file exists and is shared on every server that hosts our stores.
At this point, it is up to USPS to finish the process and provide access to the label printing functions. There is nothing further that needs to be done on the Volusion side and nothing more you, as a merchant, need to do from your end. This process must be completed by the USPS.
Please be aware that, due to USPS restrictions, you can only print labels directly from your store for some shipping methods. For an up-to-date list, please consult USPS.
Note: The labels referred to in this article are shipping, not paid postage, labels.