Found it !!!

open ftp://login:password@MyFTPsite:21 -passive -explicittls -timeout=300

Hi,

When i create a profile into Winscp GUI using FTP, TLS explicite cryptage and PASV mode on port 21 the connection is fine.

But when i try to script it, it is not working.
Here is the command i'm using :

open ftp://login:password@myftpsite:21 -passive -timeout=300

I've tried too
open ftps://login:password@myftpsite:21 -passive -timeout=300

But same issue. I think it is cause i didn't define TLS but don't know how to declare the option.
I didn't find into the Help on the site.

Thanks