Hi
There is no need to enabled FPMXLClient in developer tab for run function, EPM Execute API. It worked without activate FMPXLClinet from developer tab. There is no need to save file XLXM or XLTM the function also worked in XLSX file,regarding your problem you may be try to save the data in node label member.Check the context and input schedule member if is there any node label member are there.
Khokan