Xcode C++ can't find namespace

I added a package, via homebrew, named cln. Using this line:

#include </usr/local/Cellar/cln/1.3.6/include/cln/cln.h> 

resolved a few issues. However, the line

using namespace cln; 

is causing an "Expected namespace name" error. I'm sure there's a simple fix. I just can't figure it out. Thanks!