In RDi,
Then started the program from a command line in another session.
RDi confirms 'Debug' perspective switch. However, I didn't get an option to start debug with update production files = *yes, so I got a DBGP0003E message.
Checking thru the joblog the root cause appears to be:
Member myfile cannot be opened while UPDPROD(*NO)
In Preferences (Window-->Preferences)
Run/Debug-->IBM i Debug
Make sure Update production files is checked.