google maps showing blank screen

It sounds like the API key you're using was generated on a different machine, which has a different debug keystore.

You will need to add the SHA1 fingerprint for the debug keystore for each dev machine you use to your API key in the developer console.

In addition to that, once you're ready to make a signed release build, be sure that you use the SHA1 fingerprint for your release keystore in the API key that goes into the release version of the google_maps_api.xml file. See here for more info.