Hi Abishek,
For communicating SFTP with PI you need to generate the public certificate in PI server Trusted cAS
and then sent the certificate to SFTP server admin to generate a finger prints,that should be configure in SFTP communication channel.
Kindly refer the below blog:
ABAP proxy to SFTP with PGP Encryption using SAP PI 7.4 dual stack
Best Regards,
Monikandan.