Unable to resolve Native Bindings MAC

Hi Chris,
We have a .a file that we recived from Third party but they only have the native libraries written in objective C. I need to use them in Xamarin.MAC project. My Bindings project does not throw any errors but my Xamarin.MAC project does Undefined symbols for architecture x86_64:
"_AudioObjectGetPropertyData", referenced from:
-[CocoaAudioUnitSource startInternalWithBuffer:] in Cocoa.a

I don't understand this I looked up to each .a file and see architecture is x86_64. Can you please give me some links with info on how to tackle this?

Thanks!