In case you are using wireless headphones, we also advise checking this article.
Please check if the microphone is enabled in your game session.
In the browser: exit full-screen mode and put the toggle switch to the right:
In the PC application: open the menu by pressing CTRL + F2. Make sure the microphone icon is not crossed out and the volume is not set to 0:
You can also test the input device in the application settings.
In the mobile browser: flip your phone to portrait mode and make sure the microphone icon is not crossed out: