****CloudFlair is a tool that will search using Censys certificates that contains the domain name, then it will search for IPv4s inside those certificates and finally it will try to access the web page in those IPs.
You can also use some service that gives you the historical DNS records of the domain. Maybe the web page is running on an IP address used before.
If you find a SSRF inside the web application you can abuse it to obtain the IP address of the server.