If you see a message in-game that states you have been mic banned you will not be able to use your mic until the duration displayed in the message has been spent.
If you do not see a message, your headset may have denied permission to record audio. To fix this please hover over the Gun Raiders app icon in the home screen, look for the 3 dots and click on the permissions tab. Once in the permissions tab make sure the button to 'record audio' is turned off and back on to fully reset the function.
You will then need to check if your mic is enabled on both your headset settings and in-game settings.