Unable to establish FTP connection to Plesk server: Insecure server, it does not support FTP over TLS

Connect to the server via RDP.

Open Internet Information Services (IIS) Manager at Start > ​Windows Administrative Tools page.

Go to server_name > Sites > 203.0.113.2 > FTP SSL Settings page.

In the drop-down menu select Plesk as SSL Certificate:

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Press Apply to save changes.