SSl works for frontend but not for backend - express

Question

I have a MERN stack website which i use nginx to serve. My backend server is running on port 5000 over http. SSL works fine for my frontend, but i cant make https requests to my express server. How can i solve this issue? Should i use another SSL for my backend?
This is how my express server.js looks like:
const express = require("express");
const dotenv = require("dotenv");
const routers = require("./routers/index");
const connectDatabase = require("./helpers/database/connectDatabase");
const path = require("path");
const cors = require("cors");
// Environment Variables
dotenv.config({
path: "./config/env/config.env",
});
// MongoDb Conenction
connectDatabase();
const app = express();
// Express - Body Json
app.use(express.json());
const PORT = process.env.PORT;
// CORS
app.use(cors());
// Router Middleware
app.use("/api", routers);
app.listen(PORT, () => {
console.log(
`App Started on PORT: ${process.env.PORT} : ${process.env.NODE_ENV}`
);
});
and this is how nginx/sites-avaliable/my-site.com looks like:
server {
root /var/www/my-site.com/html;
index index.html index.htm index.nginx-debian.html;
server_name my-site.com www.my-site.com;
location / {
try_files $uri /index.html;
}
listen [::]:443 ssl ipv6only=on; # managed by Certbot
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/my-site.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/my-site.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = www.my-site.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = my-site.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80;
listen [::]:80;
server_name my-site.com www.my-site.com;
return 404; # managed by Certbot
}