Proxy crashing the site?

I have a website linked to a specific server and the proxy for the domain has been activated
Now I will create a subdomain. This subdomain will be linked to another server and the DNS A will be registered
Name (required) = The name I chose
IPv4 address (required) = IP of the new server (different from the main domain server)
The proxy has been activated

The problem here now is that when I activate the proxy in the subdomain, the page does not work and it appears to me that the error is in the host?
When the proxy is closed, it works properly and well?

Is there any explanation guys and is there a solution to this?

Please guys if anyone has a solution help me.

Hey Ghazi, can you share a screenshot of the error or the subdomain you’re referring to?