title: Setting google_app_id without google_play_services.json or gradle
body: <blockquote>
    <p>02-17 18:16:09.870: E/GMPM(12680): GoogleService failed to initialize, status: 10, Missing an expected resource: 'R.string.google_app_id' for initializing Google services.  Possible causes are missing google-services.json or com.google.gms.google-services gradle plugin.</p>
  </blockquote>
  
  <p>I'm trying to remove this error log. I could find some advices about solving this kind of problems using <strong>google_play_services.json</strong> file like this link :
  <a href="https://stackoverflow.com/questions/34365369/googleservice-failed-to-initialize">GoogleService failed to initialize</a></p>
  
  <p>But my project doesn't use gradle so I'll add google_app_id in my strings.xml. Now I'm confused. What exactly is google_app_id? Somebody says it's the project number, some says it's the project id... Even in google_play_services.json file there are some properties named "project_id", "project_number", "mobilesdk_app_id", "client_id" and still no "google_app_id" property.</p>
  
  <p>Is it ok with unique value of each apps? If so, it'll be working with project id or number, but I'm not sure.</p>
  
  <p>Thank you in advance.</p>