Proxy_fcgi:error

First time user webmin purchased PRO license. Having some issues and could use assistance.

[Fri Jun 19 08:45:38.940816 2020] [proxy_fcgi:error] [pid 213:tid 14] [client ] AH01079: failed to make connection to backend: localhost

on the Browser I get;

Service Unavailable

The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

If I create a file Index.html on the root directory the site works. However when I deploy WordPress script, I get the errors shown above. Any idea on how to fix this?

Thanks