nginx reverse proxy not serving local domain correctly

Question

I want to resolve a few domain names locally in my computer. To do this I added in /etc/hosts the following line:

127.0.0.1 example.com

Then I configured nginx with the following config file example.com.conf

server {
      server_name example.com;
      client_max_body_size 100M;

      ssl_certificate /home/user/certs/example.crt;
      ssl_certificate_key /home/user/certs/example.key;

      location / {
              proxy_pass https://127.0.0.1:3000;
      }

      listen 80;
}

When I got to example.com I still do not get the access that I need but if I put in example.com:3000 then it all works fine. Why isnt the port number not being correctly parsed in the proxy?

I am using Ubuntu 18.04 and nginx 1.14