ofxSocketIO ld returned 1 exit status

I’m trying to compile a project on raspberry pi that runs on the mac perfectly. i’m getting

ofxSocketIO.cpp:(.text+0xd4c): undefined reference to `sio::socket::emit(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, sio::message::list const&, std::function<void (sio::message::list const&)> const&)'
collect2: error: ld returned 1 exit status

I undertand that this is a linker problem and I have tried to move the file to the same dir and change it from #include <sio_client.h> to #include "sio_client.h" to see if it can link it but it does not. but noting. what could this be