N2M_RELATION_ADD is a standard SAP function module that performs functionality. This is available within standard R/3 SAP systems depending on version and release level.
Below are the pattern details for this FM showing its interface including any import, export and tables parameters. There is also a list of Exceptions and for your convenience any standard documentation available. All this information and more can also be viewed if you enter the function module name N2M_RELATION_ADD into the relevant SAP transaction such as SE37 or SE80.
CALL FUNCTION 'N2M_RELATION_ADD' " EXPORTING i_kzsto = " kzsto Reversal, return delivery, or transfer posting it_chvw_inc = " tt_chvw_inc Table Type for CHVW_INC . " N2M_RELATION_ADD