1.Turn on the virtuemart debug informationgo to components>virtuemart>configuration>configurationand set the parameter Enable debugging messages to" for all"
2. Go to the frontend The request as well as the response from USPS are displayed
You may get this response:
<?xml version="1.0"?><Error><Number>-2147219100</Number><Source>Rate_Respond.;clsRateV4.UnpackRateNode;SOLServerRates.RateV4_Respond</Source><Description>Missing value for ZipOrigination.</Description><HelpFile></HelpFile><HelpContext>1000440</HelpContext></Error>
Missing Zip origination means that you have not entered your shop information. USPS needs this the ZIP origination, and the ZIP destination, in order to give the correct quotes.
Go tocomponents>virtuemart>Shop>Shop and fill in the informations on the tab "Additional informations"