if you want to use Location Sharing feature you have to enable Google Maps SDK in order to make it working.
Enable APIs and Services
Search for Maps SDK for Android and enable it

go back to Google Developers Console's Main Home Page then go to 'Credentials'
copy the 'Android key' that normally starts with AI

build.gradle(Module:app) and change the maps_api_key value to the key that you copied from Google Consolego to Foursquare's Website and create a New Account then fill the required fields

choose the plan you want

if you are on FREE plan it's Highly Recommended to add your Payment Method to increase the limits, but if you want to test the app you can skip this by clicking on 'Return to my Apps'

finally you will get your Client ID and Client Secret

now go to Android Studio > build.gradle(Module:app) and change the foursquare_client_id and foursquare_client_secret values to the keys you have gotten from Foursquare
then click 'Sync Now' at the top