Why we can't transfer file via sftp using planned actions. And why we can transfer manually using the same script.

Yeah this is pretty weird - can you take a look at the FME Server Process monitor log? This should show the actually errors returned by the smtp call rather than just the error code:

logs>engine>current>fmeprocessmonitorengine.log

Is there a difference between directory location on Linux and Windows ? Because we are on Linux.

Thanks.

The path is from the user interface and is the same on windows and linux (for the UI). It could be different in different FME versions though. This is from FME Server 2020.

here's some more info about where the logs are

https://docs.safe.com/fme/html/FME_Server_Documentation/ReferenceManual/About_Log_Files.htm