Trying to log in with valid FTP user credentials, the following error is shown:
503 User can not login. Home directory inaccessible
Custom FTP autorization rules configured in IIS.
These rules conflict with the rules added by PPA in
FTP Authorization rules from IIS at IIS - server_name - FTP Authorization rules - empty the list of rules.
To prevent the issue, please do not customize the FTP settings configured by PPA/Plesk in IIS.