If you use Google Play services, you might have to give them your Android application key fingerprint. To get your key fingerprint, you can use the following commands:
keytool -list -v -keystore <keystore_name> -alias <alias_name> -storepass <password> -keypass <password>
You should see something like this:
Alias name: com.mastertechapps.awesomeappCreation date: Mar 14, 2017Entry type: PrivateKeyEntryCertificate chain length: 1Certificate[1]:Owner: CN=Nathanael Anderson, OU=Mobile Applications, O=Master Technology, L=Somewhere, ST=WorldWide, C=WWIssuer: CN=Nathanael Anderson, OU=Mobile Applications, O=Master Technology, L=Somewhere, ST=WorldWide, C=WWSerial number: 2f886ac2Valid from: Sun Mar 14 14:14:14 CST ...
