Variable substitution error

Hello All,

Below is my source structure:

<Messages>

<Message1>

<MT_BILL> (0...*)

<RECORD> (1....*)

<FILENAME> (1...1)

If using variable substitution for the filed FILE NAME which is in the source structure.

This is the declaration I used in channel:

payload:MT_BILL,0,RECORD,1,FILENAME,1

But i am getting this error in channel monitoring

DynamicConfigurationException: Error during variable substitution: com.sap.aii.adapter.file.varsubst.VariableDataSourceException: The following variable was not found in the message payload: var

Can anyone help me here

Regards,

Moorthy