Trouble in setting up Google assistant by voice

I want to set up Google Assistant on my Samsung Galaxy Tab A9+ tablet, but I’d like to activate it using the voice command “Hey Google” or “OK Google.” It’s not working, though—everything is enabled, from Voice Match to Google Assistant to the basic settings—but it’s as if it’s not listening to the command at all. The microphone doesn’t activate even though I’ve granted permission. Has anyone else had the same problem? I don’t want to have to use it just by pressing the home button...