Lets talk

I had combined react app to api by

app.use('/', express.static('client/build'))

and some start script you will find in package.json.
To run it for developing you had to change some code.

This is the ui of my chat app

start

node index.js

if you have nodemon

nodemon index.js

for developing

you have to change axios base url at https://github.com/tanay-pingalkar/LetsTalk-chatapp/blob/main/client/src/components/axios.js and endpoint at https://github.com/tanay-pingalkar/LetsTalk-chatapp/blob/main/client/src/components/roomChat.js to localhost:9000

run client

cd client
npm start

run server in another terminal

nodemon index.js thats it

to run changes in combined mern app

reset all changes we had made
then
cd client
npm run build
cd ..
nodemon index.js