Hi Gayathri
If your receiver channel is using RFC, it will expect a payload in RFC-XML format (refer message protocol section in link below).
Configuring the Receiver RFC Adapter - Advanced Adapter Engine - SAP Library
Without mapping, there is no way you can convert the payload to RFC-XML format unless it is already in that format when it is placed in the source SFTP folder by the third party.
I'd suggest you check with your integration lead or technical architect about the design, as an SFTP->RFC bypass scenario does not make sense.
Regards
Eng Swee
