In order to pull in USPS shipping rates to the shopping cart for an InfiPlex shopping cart, you first have to register for the USPS Web Tools. Click here to register... https://www.usps.com/business/web-tools-apis/welcome.htm. Use your domain name for the question What is the Web site address (URL) of the site that will be hosting the USPS Web Tools?

You only need to do the first step of registering. The other steps pertain to labels, InfiPlex uses either the stamps.com or EasyPost integrations for labels (see the Live-Labels tab of the shipping settings for more information).

After you register, you will be sent an email from USPS with your userid and password. Enter that userid and password on the Live Rates tab of the Shop Shipping settings (Shop --> Settings -->Shipping -->Live-Rates)