Hi,
You can achieve this using I_STEP = 3 in user exit. The variable should be of type Input and the write logic to check v_buper = 0 or not in user exit code .
CALL FUNCTION 'RRMS_MESSAGE_HANDLING'
EXPORTING
I_CLASS = 'RSBBS'
I_TYPE = 'I'
I_NUMBER = '000'
I_MSGV1 = 'This is the first period so please exit'.
CALL FUNCTION 'RRMS_MESSAGES_SHOW'
EXPORTING
i_handle = n_handle.
Please find below attached SAP document which explains clearly step by step the above logic which i explained in document - How to .