vercel deployment .env not found

I am doing a deployment in vercel. Currently change in scripts the settings for npm start and add npm run start:staging since I have 2 environments. Add the variables inside vercel and modify the build commands
env-cmd -f .env.staging react-scripts build and the development command a: env-cmd -f .env.staging react-scripts start. The package.json file looks like this:

"scripts": {
    "start": "env-cmd -f .env.development react-scripts start",
    "start:staging": "env-cmd -f .env.staging react-scripts start",
    "start:production": "env-cmd -f .env.production react-scripts start",
    "build": "env-cmd -f .env.development react-scripts build",
    "build:staging": "env-cmd -f .env.staging react-scripts build",
    "build:production": "env-cmd -f .env.production react-scripts build",
    "test": "react-scripts test",
    "eject": "react-scripts eject"
  },

However it gives me the error in the deployment:

Error: Failed to find .env file at path: .env.staging
    at getEnvFile (/vercel/path0/node_modules/env-cmd/dist/get-env-vars.js:40:19)
Error: Command "env-cmd -f .env.staging react-scripts build" exited with 1

Obviously this started to happen when the files

• .env.staging
• .env.development

they were pushed to the repository and I removed them from the cache because .gitignore was not preventing their upload. What could be happening?

Taking into consideration that you don't have the .env files in your repo (which you shouldn't (source)) - Vercel can't read them.

You need to specify the Environment Variables specific to deployments.

How do I set up a staging environment on Vercel?

Edit

I suggest reading the Environment Variables article on the Vercel Docs if you want to learn more.