In Daniel 3, what were people commanded to do when they heard the music play?

Answer: Worship the golden statue

At the sound of the horn, flute, lyre and other music, all were to fall down and worship Nebuchadnezzar's golden statue or face the furnace.

“As soon as you hear the sound of the horn, flute, zither, lyre, harp, pipes, and all kinds of music, you must fall down and worship the golden statue that King Nebuchadnezzar has set up.”— Daniel 3:5 (BSB)