Check the ringer switch on the external side of your device (iPhone/iPad)

Check the media volume of your device

Make sure that any "do not disturb" modes are not switched on

If you don't have an account and you're playing using a local player, try turning off WiFi and Cellular Data when playing (this resolves the issue in 90% of the cases)

Force-quit the app, then open it again if the sound stops - on both Android and iOS, please make sure you swipe the app away from the app switcher

If you have any music, video, or voice/video call apps open, please force quit these before opening the game. These include music streaming services, video streaming services, websites with videos or ads playing, communication apps like face time, Skype, Messenger, WhatsApp (etc.), mostly if you have recently used them for a voice or video call.