Accessing reverse proxy by domain.com/subdomain

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I am running a reverse proxy through nginx on my server.

The solution I use with DNS Resolver - see screenshot - works with my reverse proxy if I use "https://subdomain.domain.com" but if I use "https://domain.com/subdomain" it doesn't work.

However If I use "https://www.domain.com/subdomain" it works.

If I try to connect to "https://domain.com/subdomain" i get cert authority error since it tries to connect to my pfSense instead of nginx on my server.

Can I get "https://domain.com/subdomain" to work in pfSense? Or should/could I redirect the request from that domain to www instead?

Thanks in advance