I just went to your site to check the settings and figured out that you didn't enter Length x Width x Height value in the USPS shipping plugin configuration. Please go there to enter that value and test again.
Is there any documentation on the USPS plug in
I don't see how I am supposed to configure the Dimensions L x W x H in the USPS Plugin,,,, if all the product orders may have different package/box dimensions. How can you have a one size fits all configuration? Different customers will be ordering different products in different quantities, making the final dimensions of the package to be shipped different possibly every order? And can you give an example of how it is supposed to be done, if there is no documentation