The original version of the website contained a link to an old version of the Arduino code that isn’t correct. You can download the new version that should work here. Or if you’d rather update it yourself, you just need to copy and paste the following code inside the “loop” function:
serialCheck(); //Check for new serial input
if (stringComplete){ //Check if string is complete
parseInput(); //Run parseInput function
} //end if
Thanks to Ben Mellors for noticing the error