Error When Compiling an Example with ESPHelper

I’m trying to compile the an example from ESPHelper library and it’s giving me this error and i’m scratching my head:

ESPHelper_ID1556/src/ESPHelper.cpp: In member function ‘void ESPHelper::setMQTTCallback(std::function<void(char*, unsigned char*, unsigned int)>)’:
ESPHelper_ID1556/src/ESPHelper.cpp:832:16: error: cannot convert ‘std::function<void(char*, unsigned char*, unsigned int)>’ to ‘void ()(char, uint8_t*, unsigned int) {aka void ()(char, unsigned char*, unsigned int)}’ in assignment
_mqttCallback = callback;
*** [.pio/build/my_build_env/lib877/ESPHelper_ID1556/ESPHelper.cpp.o] Error 1

This is on PlaformIO as part of Code on Mac OS. Any ideas what i’m doing wrong?