I am making a website by using Flutter but I am facing a problem when I deploy the website using Firebase hosting this screen is facing me

so I have searched for a solution for this problem and everyone says that I have to run npm run build before deploying but when I run this command this error faces me

npm error Missing script: “build”

I have searched before I posted this question but every question is about react not flutter I used the solution that the people recommended and it did not work for me