Tax codes are transferred to FSM using the corresponding sending transaction - /PACG/ECM_ATAXC – Allowed tax codes.
(S4)PACG 200 SP09 You can navigate to the sending transaction using the button Send to FSM, placed on the toolbar.
Tax codes are used for invoicing, purchase order, sales order and sales quotation in FSM.
Make sure that object TAXCODE is assigned to your company in /PACG/ECM_NOAS - No Object Assignment, otherwise tax codes can’t be transferred.