This error can occur due to one of the following reasons:

• Apache "mod_rewrite" module is not ON. To fix this issue make sure that Apache module mod_rewrite is turned on in website builder virtual host. If you use nginx server for website builder, make sure that all required rewrite rules are set in nginx configuration for website builder.
• Wrong website builder plugin is installed. If you have multiple Site.pro brands using different website builder domains, possibly you installed plugin from the brand where website builder domain differs from the one that you installed for website builder plugin. You need to re-install plugin on cPanel using plugin installation guide link from a correct brand.
• Builder domain has changed. If you changed website builder domain when website builder plugin was already installed on cPanel, this error can occur. Re-install website builder plugin to fix this problem so that cPanel gets new website builder domain from Site.pro license.
• Builder domain is locally resolved to incorrect IP. Possibly you have custom record specified in file "/etc/hosts" which points website builder domain to a different IP. As a result website builder plugin API call fails. Make sure that website builder domain on your cPanel server is resolved to a correct IP address.