This was a doozy today. I signed up for USPS Web Tools, plugged my User ID and test server details into my Magento Development site, and was rudely greeted with the error:
“API Authorization failure. RateV4 is not a valid API name for this protocol”
My initial symptom: I didn’t see any USPS rates in my front end. Enabling debugging allowed my to see the error in /var/log/shipping_usps.log.
The problem is that the USPS test servers didn’t support RateV4. So, you email USPS support to enable production server access for your USPS User ID. And we’re all set!