Hello Dinamol,
1) Have you added any authorization in the screen enhancement?
Execute your program and check in SU53 does it has any authorization failure.
2) Your screen enhancement is done in which screen, SAPLMIGO 0001 or in any other screen, if you can read the code inside the MIGO_DIALOG it is caling screen 0001, in case if your enhancement is not in this screen then obviously the custom field won't appear using MIGO_DIALOG.
Regards,
Tp