In order to use the Nearby Notification module, you need to upload the Google service account key. You can upload the JSON file if you login as the system owner, and go to
Settings > Google.
Start here to create a new project for your proximity service key: https://console.developers.google.com/apis/dashboard.
And follow the steps in this video to download the JSON key file: https://youtu.be/RtbEIOtCwAA.