Hello rahhaoui mohamed,
On of those fields in the printscreen should be filled in if not I should display an error.
Solution (Tested)
User Exit : QQMA0014 Function Exit: EXIT_SAPMIWO0_020 Include : ZXQQMU20
Code to be used
IF I_VIQMEL-QMART = 'M4'.
IF I_VIQMEL-GSBER IS INITIAL AND I_VIQMEL-PROID IS INITIAL AND I_VIQMEL-KOSTL IS INITIAL.
MESSAGE 'One of the fields of BusArea, CostCtr or WBS Element in the Location tab is mandatory' TYPE 'I'.
RAISE EXIT_FROM_SAVE.
ENDIF.
ENDIF.
You'll get this pop-up, when all these fields are empty.
The first and last lines of the code makes this code confined to Notification type M4 only. (You may change as per your need)
Jogeswara Rao K