not able to npm run dev

[Yashparkar06]

It gives the following error:

mern-ecommerce@1.0.0 dev
concurrently "npm run server" "npm run client"

[0]
[0] > mern-ecommerce@1.0.0 server
[0] > nodemon server.js
[0]
[1]
[1] > mern-ecommerce@1.0.0 client
[1] > npm start --prefix client
[1]
[0] [nodemon] 2.0.22
[0] [nodemon] to restart at any time, enter rs
[0] [nodemon] watching path(s): .
[0] [nodemon] watching extensions: js,mjs,json
[0] [nodemon] starting node server.js
[0] Server is running on port 3000
[0] The uri parameter to openUri() must be a string, got "undefined". Make sure the first parameter to mongoose.connect() or mongoose.createConnection() is a string.
[0] [nodemon] app crashed - waiting for file changes before starting...
[1]
[1] > client@0.1.0 start
[1] > react-scripts start
[1]
[1] Something is already running on port 3000.
[1] npm run client exited with code 0

[ashraf-kabir]

set up & fix your mongoDB

[Yashparkar06]

I did everything still it's not able to run the application even though my MongoDB is working completely fine. The website is running but the database isn't reacting(after signing up nothing happens it remains in the same state as a static website)
Please help me with this if you want I could send you my whole code my end-sem project submission is really close🙏🙏