To debug a script go to the dialog "Manage scripts", select the desired script, and click on the button "Debug". The button debug is visible only in the experimental version of Banana Accounting.
After the debugger is started click one or more times on the key Shift-F11 until you see the call of the function "exec(inData)", then click F11. At this point you are in the main function of the script.
Banana Accounting use the Qt Script Debugger to debug the scripts.