1. Unable to add the server as FTP Storage for backup on Plesk for Linux server:
PLESK_ERROR: Erro: Unable to access to the storage: Transport error: unable to list directory: Curl error: (30) FTP: command PORT failed: Last FTP request: PORT 192, 168, 0, 64, 210, 240
Last FTP response: 501 Server accept argument.
Make sure you have entered the correct storage credentials. You can check them independently with the command: curl -v -P - -u user 'ftp:203.0.113.2///'
2. Hostname or public IP 203.0.113.2 of FTP server is set in FTP server hostname or IP section in Plesk > Tools & Settings > Backup Manager > FTP Storage Settings
3. Both servers are behind NAT.
Incorrectly configured FTP connection for servers behind NAT: it cannot connect using public IP or a hostname that resolves to a public IP. Only internal IP can be accepted.
Specify internal IP address for remote FTP storage in FTP server hostname or IP section in Plesk > Tools & Settings > Backup Manager > FTP Storage Settings