IOS build problem "exit code 1"

hi
i am currently building vr apps using GVR package. target platform is for android and IOS.
the android version was successfuly build without problem. but i am facing problem when building for IOS. this is the error i get:

"clang: error: linker command failed with exit code 1(use -v to see invocation)"

(please see attached image )

we did a lot of research but still no solution can solve the problem.
any help will be really appreciated.

thanks