Undefined symbols for architecture armv7: "_OBJC_CLASS_$_FIRApp"
<p>I am integrating Firebase in my app according to the instructions and added [FIRApp configure]; in the code however, while compiling the app I am getting the following error:</p>

<p>Undefined symbols for architecture armv7:
  "_OBJC_CLASS_$_FIRApp", referenced from:
      objc-class-ref in AppDelegate.o
ld: symbol(s) not found for architecture armv7</p>