I watch a lot of YouTube slot channel personalities having the same problem. You're tapping the button but the volume won't turn up. Or, you're in a bonus and have a choice of three symbols but no matter how many times you hit your choice, it won't respond. This is because the machine needs calibrating. Slot machines are kind of like guitars and they can "go out of tune." It happens a lot with very popular slots, especially those subjected to repeated banging in tournaments. Some people almost crack the screens with their rings. Machines don't like that and they retaliate.