Expo Push Notifications: "Error: Couldn't get GCM token on device."

I'm trying to receive push notifications with my Expo app, but at this line, the mentioned error is thrown:

token = await Notifications.getExpoPushTokenAsync();

I already tried:

• setting up a FireBase account and linking the server API key withexpo push:android:upload --api-key <token>
• downloading the google-services.json, linking it in app.json and making sure that android.package is correct
• logging into my expo account with expo login
• upgrading Expo to the newest version
• building the app and running it as a standalone app on a physical device

Unfortunately, nothing worked and I'm running out of ideas. Any suggestions?