Joomla FTP Configuration Issue – Connection Failed Despite Correct Credentials

“Hello
can you please specify what to put into the Joomla FTP parameters?
We tried every possible variation (including the SSH2 from Frederic Gilles) – but always get “FTP connection failed”
We checked via Filezilla if the FTP credentials are correct – they are.
We created a separate FTP-account so that the conection leads directly into the Joomla root directory.
Shall we leave the FTP base directory field empty or put a / ?

Can you please help?”