there is no './server/config/key-firebase'

[gorkemuz]

in src/index.js there is imported file "import {key} from './server/config/key-firebase';" but there is no file like that. so no one can access the app.

[bariscc]

This is probably an ignored file because it contains a key.
You should get your own key from https://firebase.google.com/
Then you can remove the import and use your own key
or create the said file, store your key in it and export it.