Question - How do we debug sapscript?
Answer -
First we need to put Break point in Print program where ever you want to stop the execution.
After in SE71 give your form name and go to Utilities-->Active De-bugger.
Then go to your transcation like VF03(for Invoice or Credit memo) etc to see the print preview or print the form execute it.
When you execute it the the form Debugging will get activated and you can see your Form execution step by step.