On Android 9 and above, Google Assistant may interfere with Zello's ability to process external PTT buttons. Follow the steps below to turn off Google Assistant. 

1. Open your device's settings and tap Google.
   
   
   
2. Follow the pathway Settings for Google Apps > Search, Assistant & Voice
   
   
   
3. Go to Google Assistant > Hey Google & Voice Match
   
   
   
4. Turn off the Hey Google toggle.
   Note: When Google Assistant is off, the toggle is gray. When it's on, the toggle is blue.