Submit your program into batch and make sure it is held. Do this by either holding the job
queue that you are submitting the job to, or use the HOLD(*YES) option on the SBMJOB command.
Use the WRKUSRJOB and display the job you with to debug with the display job option (5).
Write down the user name, job name and number.
Start a service job using STRSRVJOB entering the name, job name and number from the previous
step.
STRDBG PGM(YOURPGM) - Press F12 to exit the source display (Sorry, can't enter breakpoints yet).
Release your submitted job by releasing the job queue or the job itself.
A display will appear asking you to press F10 function key. Press F10 and you will be brought
to a command line.
Enter DSPMODSRC and enter your breakpoints.
Leave source display and command line by pressing F3 until you are back to the screen that asks
you to press F10 to enter breakpoints.
Press Enter to start your job.
After that the job begins running and stops at the first breakpoint reached.