Mac nginx: [emerg] bind() to 0.0.0.0:8000 failed (48: Address already in use)

I am using Nginx to run both the frontend and backend from the same PC.

Frontend: React (localhost:3000)

Backend : GO-Lang (localhost:8080)

You can expect CORS error when you try to access BE APIs from your FE code.

To overcome this I used nginx to create proxies for FE and BE on Different routes but on the same port (localhost:8000)

FE: /

BE: /server

nginx.conf

upstream server {
server localhost:8080;
}

upstream client {
server localhost:3000;
}

server {
    listen 8000;
    server_name localhost;

    location / {
        proxy_pass http://client;
    }

    location ~ /server/(?<section>.*) {
        rewrite ^/server/(.*)$ /$1 break;

        proxy_pass http://server;
       
    }
}

I stopped the nginx with sudo nginx -s stop

Closed terminal

Quit terminal completely

But didn't shut down my PC

1. Today I tried some other configs with the same port (8000) and got the error mentioned in the title.

2. So used a different port everything worked as expected.

3. But when I reverted my config to the above config again. It is showing the error mentioned in the title.

The problem

1. What I observed is all the ports I used in step 2 are occupied now and I am not able to use them although I have stopped all the servers earlier.

2. After reverting back to the initial config even though the port I am trying to use is 8000 it still says that the port is occupied.

How can I use my port 8000 again?