I've followed the instructions on getting a username and the correct testing api for USPS shipping. I've entered this information in, and saved.
I go to checkout using my sandbox info, and i'm getting "Shipping=fail" in the address bar and an error message saying that either my billing/payment info is invalid and it gives the link to the checkout page to try again.
When I go back into my cms, and disable shipping. I use this same info to checkout, and everything goes through completely.
I've tried checking test mode, and unchecking test mode. I've also tried both http and https links the email gave me to try. I even requested permission for the address api (the link it gave me after I signed up for my usps username).
I am at a loss at what I am doing wrong.