title: Failed to install pod: Undefined symbols for architecture x86_64
body: <p>According to <a href="https://developers.google.com/admob/ios/mediation/facebook" rel="noreferrer">AdMob documentation</a>, in order to integrate with facebook audience network I need to install this pod:</p>
  
  <pre><code>pod 'GoogleMobileAdsMediationFacebook'
  </code></pre>
  
  <p>When I try to install it, I received an error:</p>
  
  <blockquote>
    <p>Undefined symbols for architecture x86_64:   "_OBJC_CLASS_$_GADUnifiedNativeAdView", referenced from:
          objc-class-ref in FacebookAdapter(GADFBNativeAd.o) ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed
    with exit code 1 (use -v to see invocation)</p>
  </blockquote>
  
  <p>Unfortunately I didn't find a solution for this issue.</p>
  
  <p>Thanks. </p>