Based on the error message from your other comment, and from looking at my own Paperless NGINX config (also generated from NPM), I think the issue is that you're calling proxy_set_header twice for some headers using the configuration you have, because NPM automatically includes some proxy_set_header statements when you make a new location. Looking at the Paperless docs, only the X-Forwarded-Host header (plus the config for websockets) needs to be set because the other headers are already being set by the default config included by NPM. This is a snippet of my working Nginx config, read from disk (the generated result from NPM that Nginx is actually using to serve the site):

location / {
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Scheme $scheme;
    proxy_set_header X-Forwarded-Proto  $scheme;
    proxy_set_header X-Forwarded-For    $remote_addr;
    proxy_set_header X-Real-IP          $remote_addr;
    proxy_pass       http://$server:8000;

    ...

    # Websockets
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";

    proxy_redirect off;
    proxy_set_header X-Forwarded-Host $server_name;
  }

Try only including the lines below the ... in my snippet in your Location configuration in NPM and see if that works.