For File Based Authentication, please create a folder structure "/.well-known/pki-validation/" under the root directory. Som (S)FTP programs won't be displaying folders beginning with a dot by default, it might be necessary to enable the "show hidden files" setting.
Under Windows/IIS you cannot create folder names including the dot in the name, instead you have to create a virtual directory, see also: https://msdn.microsoft.com/en-US/library/bb763173.aspx.
In Mac OS (OSX) Server the .well-known functionality needs to be enabled inside Apache configuration. For details see https://www.interssl.com/en/knowledgebase.php?action=displayarticle&id=774
Then create the file using following details or download the Authentication file by clicking the "Download Auth File" button and place it in the "/.well-known/pki-validation/" of the HTTP server, like so: http://example.com/.well-known/pki-validation/<filename> for www.example.com/example.com and http://subdomain.example.com/.well-known/pki-validation/<filename> for SSLs including a subdomain eg. subdomain.example.com.
It may take some time for file to be automatically validated and cert to be issued by Certificate Authority
From August 19th 2020, SECTIGO issues SSL certificates with a maximum lifetime of 398 days (13 months) as specified by CA/Browser consortium. SSL certificates with a longer lifetime must be re-issued annually (free of charge). You'll receive reminders via e-mail. SSL certificates issued before August 19th 2020 remain valid until their planned expiry date. Code Signing & S/MIME certificates are not affected and remain valid until their planned expiry date.
