To resolve this issue, you need to create a .env.local file in the root of your project.
1. Copy the contents from the .env.local.example file.
2. Paste them into a new file named .env.local.
3. Fill in the values with your own Firebase project credentials, which you can find in your Firebase project settings.
After you have created and saved the .env.local file, you will need to restart the development server for the changes to take effect.