When rating any USPS service with no special services selected, the error message "USPS Failed to Rate" is displayed.
The diagnostics logs will show an additional error of "Invalid URI: The hostname could not be parsed."
If you are trying to ship a regular, non-ERR shipment, select carrier "PB Shipping API - USPS".
Use the USPS carrier for ERR shipments only, with "Certified" and "Electronic Return Receipt" selected.
UPDATED: June 02, 2021