The owner of the executable file, cybAgent.bin, needs to have appropriate permissions on the source file (upload) or the target file (download).
Make sure those permissions are in place. When the job runs, the owner of the agent process that does the file transfer requires the correct permissions to be set.
Therefore, the logon of the service of the agent needs to have write permission on the target file.
By default, FTP/SFTP/SCP are internal to the agent, so they are executed as the user that started the agent.