Dynamic file name from input payload (RFC 2 flat file)

Hi,

I have an RFC to flat file scenario. The output flat file has not an XML structure, it's just a plain text file generated with abap mapping.

In my source interface (RFC), I have a field called <FILENAME>, I want to use the value of that field to create the target file using dynamic file name. But if in variable substitution I use payload:ZRFC_NAME,1,FILENAME,1 It doesn't work because the dynamic variable substitution try to access to output payload, not the source one...

What can I do?