Before you can use the shipping plugin to acquire "real-time" shipping rates from the United States Postal Service (USPS), you must obtain a valid account and license.
Step 1: Register with USPS
Visit the USPS website and register your company to obtain a username and password and agree to the terms and conditions of the USPS at this URL: https://www.usps.com/business/web-tools-apis/welcome.htm. The US Post Office will email your username and password once they have completed your application.
Step 2: Licensing
Using this software, you agree to use it abiding to the USPS license.
Step 3: Activating your License
Once you have your username and password you will then need to contact USPS's Internet Customer Care Center (ICCC) and have them set your profile to the Production Server. Simply tell them you have the USPS Shipping Plugin from COMCITY/SalesCart.
The ICCC is manned from 7:00AM to 11:00PM Eastern Time.
E-mail: icustomercare@usps.com
Telephone: 1-800-344-7779 (7:00AM to 11:00PM ET)