OK Google Voice Match not working
If you have a Bixby or S Voice installed and would prefer to use Google's voice assistant instead, your best bet might be to disable Bixby or S Voice on your device entirely. And if you’ve downloaded Alexa, Cortana, or any other voice assistant on your phone, either disable or delete it.
Also, make sure the Google app is updated to the latest version. Also make sure to grant all permissions for the Google app by going to Settings > Apps > Google app > Permissions (the path may differ from model to model)