Okay, so the customizing should be fine.
You said COR6 but than refer to BAPI to post HEADER confirmation. So to post COR6 via BAPI the correct one to use is BAPI_PROCORDCONF_CREATE_TT.
To propose the goods movements run the proposal BAPI before
It's BAPI_PROCORDCONF_GET_TT_PROP or for the header confirmation BAPI_PROCORDCONF_GET_HDR_PROP
this will propose the goods movements in the same logic
BR Sabine