Nginx try_files loads blank page when passed with variable path

I am setting up nginx to work with a React SPA. The page loads fine when I do not include a variable path (/rsvp/). But when I try (/rsvp/S0mEtH1NG), it will download the index, manifest, css files... but it doesn't actually apply those things to the index.html. I pretty much just see my index.html with nothing actually loaded.

My config looks something like this:

server {
    listen 80;
    server_name something.com;

    location / {
        root /srv/something.com/webroot;
        index index.html;
    }

    location /rsvp {
        alias /srv/rsvp/build;
        try_files $uri $uri/ /rsvp/index.html;
    }
}

If I have try_files $uri $uri/ /index.html, it will load the index.html of the root (/) but with a similar issue in that it doesn't use any of the css.

Thanks for help, its much appreciated!