In case you are using wireless headphones, we also advise checking this article.
Browser
Press right-click on the browser tab with the Boosteroid website and check if Boosteroid is unmuted.

Try to use the Incognito mode in the Google Chrome browser (CTRL+Shift+N).

Try checking if the browser is updated to the latest version (e.g. you can do that by opening the chrome://settings/help link in Google Chrome)

Try to reboot your device.
If none of the tips resolved the problem, please contact our support for further instructions.
Windows/Linux application
Try checking the output device in the application settings by pressing the "Play" button. You can also check different output devices.

Try checking what volume the application has in the Volume mixer.

If these tips didn't resolve the problem, please contact our support for further instructions.