Material master Inbound - Zfield is not updated

Hi Experts

I am calling an inbound functional module for material master update IDOC_INPUT_MATMAS01

I have added custom fields in MARA ( using append structure) and I also have custom segments in IDOC to update the custom fields in MARA .

I have done coding to move the segment data to MARA in exit - include name ZXMGVU04

case f_cust_segment-segnam.

when 'Z1MARA1'.

move f_cust_segment-sdata to z1mara1.

move-corresponding z1mara1 to f_mara_ueb.

Values are moved perfectly and able to get the segment values populated in IDOC . IDOC part is fine.

But it does not update custom fields in the MARA table.

Please advise.