I was having a frustrating time setting up Google Assistant on my Android phone, because at the part where I'm supposed to set up Voice Match by saying "OK Google" it just acted like it didn't hear me. Yet I could use voice for other Google and non-Google things.
I tried many things, then I found this in a user forum somewhere:
Uninstall updates for the Google app from Settings -> Apps -> Google -> ... (tap the three dots on top right) -> Uninstall updates. Now setup Google voice. Once successful, you can update Google app back to the latest version.
