If you are getting to the shipping failure page then you will need to add in the full request and full response bindings for your shipping service provider. On your shipping failure page go to the bindings and expand them to find the USPS selection, in here drag and drop the full request and full response onto the page where you would like to see them, then save the page and test it again. You should normally be doing live API testing on a live server to ensure that you are getting the same result as you will in the end environment.
As for the ip address of 127.0.0.1 you would use this in your connection file in place of localhost.