There must be a step we are missing. This is what I did:
1. I have my user ID from USPS. I entered this into the user ID
2. Here is the email from USPS. I entered both of these URLs
Depending on the API, the address to the test server is either
http://production.shippingapis.com/ShippingAPITest.dll or
https://secure.shippingapis.com/ShippingAPITest.dll. Use this information in combination with your User ID and your XML string to send a request to the USPS servers.
3. I clicked on SAVE
4. I went the the bottom of the screen and entered a zip code
5. I click on TEST
I get a new screen with the logs and it says
Authorization failure. You are not authorized to connect to this server.
I used my test program outside of XC and my login and both URLs work properly.
What steps are you taking exactly?