I suspect that you have missed out the include statement from your main.cpp file:
I've just tried that on a working package running on my test rig and can duplicate you compile error by removing the include statement. Without the inclusion of the #include <MUSES72323.h> statement, the compiler won't find or try to use the MUSES72323 library which has been installed into your package by the following statements in platformio.ini:
Geoff