Server hostname (server.example.com) is behind Cloudflare and was added to Server Inventory in Plesk 360 as https://server.example.com:8443
The following error appears under Server state in Plesk 360:
PLESK_ERROR: Connection error
The following message appears under Plesk 360 > Server > server_hostname:
PLESK_ERROR: The connection to the server server.example.com cannot be established correctly. The server is configured incorrectly or you have entered an incorrect address.
Please fix the error and press the button below to restore the connection.
Connection fails since at the moment Plesk service on port 8443 does not support restoring original visitor IPs for Cloudflare since sw-cp-server is compiled without
PAUX-3379 was created to improve the behavior.
If it is possible, disable proxy on the Cloudflare side until the issue gets resolved.
Create a domain for Plesk UI specifically (e.g. server.example.com)
Under Tools & Settings > Customize Plesk URL, select The specified domain or subdomain that resolves to the server IP address but is not used for hosting and put server.example.com
Enable restoring original visitor IP in accordance with the article below (the section Server-wide solution with Nginx enabled):
Incorrect IP addresses logged by Plesk behind load balancer, or reverse/forward proxy
Make sure that Plesk URL can be accessed via
https://server.example.com, and it is secured with a valid certificate (Cloudflare should do that automatically)
Try to re-connect the server to Plesk 360 by using https://server.example.com (without port 8443)