Getting an “Undefined symbols for architecture arm64” error while building a Unity project in Xcode 11.3

I have been trying to build my AR (Vuforia 9.2.8) Unity Project (2019.4.2f1) for iOS. But when I build the project in Xcode (11.3), I always get following error:

 Undefined symbols for architecture arm64:
   "_sampleMethod", referenced from:
       _PhotoCapture_sampleMethod_m69D10A1489308720B3C58E2357E18B623B0CFB23 in Assembly-CSharp.o
      (maybe you meant: _PhotoCapture_sampleMethod_m69D10A1489308720B3C58E2357E18B623B0CFB23)
 ld: symbol(s) not found for architecture arm64
 clang: error: linker command failed with exit code 1 (use -v to see invocation)

The error appears while building the "UnityFramework". I tried to change the build settings in Xcode and Unity but couldn't solve it. What is PhotoCapture and how do I fix this error?