The domain A is set up with Cloudflare and running correctly.
We need to set up domain B to forward the visitor automatically to domain A.
On the server where the site for domain A is hosted, there are other websites. They are sharing the same IP address.
How to set up the DNS for domain B such that the user will only be forwarded to domain A instead of other sites? Should we move the site for domain A to a dedicated server?
Create 2 DNS records, one for @ and one for www in the DNS tab of your Cloudflare dashboard. Point them both to 192.0.2.1 and then the page rule (if configured correctly) will work.
You see this message because you have no DNS record for @.