This functionality is supported only if you are using the Classic Agent.
If you are starting your standalone Java application through a Command Prompt window, close and re-open the Command Prompt window when you restart your application.
If you have forgotten to close and re-open the Command Prompt window, use the Basic Workflow bar to enable the extension again, making sure that you close and re-open both your Java application and the Command Prompt window before you click Test on the Test Extension Settings dialog box.