Some operations on file system (subdomain creation, file uploads etc) fail. The following error can be found in
System error 122: Disk quota exceeded
Cannot create directory /test.example.com: Disk quota exceeded
Cannot update WordPress plugins. The following error can be found in
stderr: Warning: Download failed. "cURL error 23: Failed writing body (353 != 1369)"
Quota limit set for the FTP user of the main domain is exceeded.
Change/update FTP user quota in Plesk > Domains > example.com > FTP access .