Hi, I have a chat in this forum about 'how data writes to ERP', may be it could help
'Hi, seems there is no any FM's in "RSPLAN, Ithink you need Planning func. /ERP/SFIN_A09_PF01" which is responsible for data retraction, only for manipulation on worksheet.
But you can find it anyway.
In Integration IBP and ERP query go to analysis- information tab, here you can see Info Provider, e.g. /ERP/SFIN_A09. Then got to RSA1 and find required Virtual provider, e.g. /ERP/COOM_V03, which Based on Function (Class) CL_FCOM_IP_IPROV_WRITABLE.
Then go to se24, put this class and drill down to required METHOD, E.G. POST_CCTR_PRIM_SEC_DATA, here you can see that BAPI_COSTACTPLN_POSTPRIMCOST is called.'