Hi,
1. Make sure you have set up the plugin right with the live API siteID and password,
2. The products need to have weight and dimensions in them,
3. In the plugin settings General tab, enable real time rates option.
4. plugin settings Rates and services tab, enable show account rates option.
If you still face issues, turn on the developer mode in the plugin settings and while calculating the shipping cost, copy and attach debug data here.
Regards,
Lorenzo