Dial pad fails when in a call

Why the dial pad fails working when in a call? I need to call a international number. It replies with an voice menus for me to key in my option with the dial pad. However, whatever I tap in the dial pad, it just won’t go to the other end. Even worse, this situation happens even when I am using gmail dialing function, hangouts or google voice in browser on my MacBook. That’s terrible!

DannyMenlo about Hangouts, v21.0.0