Transport error: unable to list directory: Curl error: Couldn't connect to server

Hi,

https://talk.plesk.com/threads/transport-error-unable-to-list-directory-curl-error-couldnt-connect-to-server.341569/

I'm using Plesk

When I try to manage my FTP Backup, I have that error :
"Transport error: unable to list directory: Curl error: Couldn't connect to server"
The server side is a OVH Cloud.
I can make a connection with FileZilla in SFTP and in SSH too with the command SFTP.

Can you tell me why I can have this error ?
I ve tried too in passive mode.. but without success.

Thx a lot for your answer.