I got to testing it and got an error. The usps api account was moved to the production server. I got the email verification from the post office. I did enter the correct credentials in shipping rules. I am using the paypal Sandbox. The items have weights in ounces. The error message is vague. It simply says:
Your transaction could not be completed due to a problem occurring while calculating shipping.
Please return to checkout and try again, or contact us.
Please help. Thank you.