Make sure you have your volume turned up. If you have an iOS device, check that your side mute button isn't switched on. Finally, try refreshing the page.
Check your internet connection or try a different web browser. Play the Key should work on all modern browsers which support the Web Audio API.
If you are on a mobile device, please turn the device sideways to play with a bigger keyboard. Otherwise, on any other large devices you should have access to around 4 octaves of notes which should cover a large and common range of notes for piano.
There can be two main reasons why there are multiple notes.
1. If you played a black key, they can be represented by both # and ♭. # is a semitone higher whilst a ♭ is a semitone lower. For example, a C# is a key higher than C which is the same as D♭ which is a key lower than D. If you are still unsure why, please talk to your music teacher to learn about sharps and flats.
2. If you played a key near the middle of the keyboard, that key may be shown in both treble and bass clef. Sometimes you'll have to read this note on either the treble or bass staff, so both are shown just in case. Again, if you are confused please consult your music teacher.
Unfortunately playing chords isn't supported as it is more difficult to be able to allow multiple keys to be played at once. If you are struggling with reading a chord, it is suggested to figure out one note at a time.
If you have some suggestion or issue that isn't discussed here, please feel free to contact me. I welcome all feedback!