If you have correctly done all the steps to configure your GoogleMap, and you just see an empty map with a [+/-] zoom control, you probably havent registered your debug key in Google APIs console.
To find your debug SHA1 key:
running a terminal inside HOME directory (Linux: /home/user/, Windows: C:\Users\user\, etc)
keytool -list -v -keystore .android/debug.keystore
It will ask you for a password, leave it empty and press enter. You will see the SHA1 key, that looks like this:
Certificate fingerprints: MD5: BA:3C:6D:7A:4C:4A:AD:3E:65:DB:53:D1:3A:23:A3:4D SHA1: B5:38:93:50:7C:EA:55:23:51:1E:BC:EE:AA:A5:6D:A8:6C:B7:16:35
To register the debug SHA1 as allowed app in Google APIs Console
Now, on Google APIs console, go to the “API Access” section and generate a new allowed key for an app. As the value, attach your app’s package name to the SHA1 key separated by a | character. Like this.:
So now, your allowed apps list should look like this:
Key for Android apps (with certificates) API key: Whatever_the_api_key_is Android apps: XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX:XX;com.example.mymapsproject B5:38:93:50:7C:EA:55:23:51:1E:BC:EE:AA:A5:6D:A8:6C:B7:16:35;com.example.mymapsproject Activated on: Date, Time
one line for the “production” signature, and another line for the debug signature. Note that the character beetween the SHA1 and the package name used to be “|” for previous versions of Google APIs, but now is a semicolon “;”.
Hope it helps!