Need secondary custom domain to forward to an innerpage

I am using Cloudflare. The subdomains aren’t working due to SSL issues. E.g. W***i.f*****n.com

Cloudflare has the DNS. It should go to the site and then a PHP file that redirects to our admission site.

That site needs a URL so can’t do in DNS. I suppose the previous site had some .htaccess rule that helped and I missed it or something like that.

In short, we need to add the subdomain to this site which we need to open in an innerpage at f******n.com/w***i (our PHP file is at f******n.com/w***i I believe).

We need this as this file helps to do the redirect to the other site.