No one can hear me!

[UgiLiz]

Just before a Zoom meeting I test my audio and it's fine. When the meeting starts sometimes I can say hello but the audio then cuts out, other times there is no audio at all.  When I test my audio outside of a meeting it doesn't work. I'm pretty sure the microphone is OK. Any ideas? (Windows 10, HP Envy laptop)

[UgiLiz]

Just to add...

I've just had a successful meeting using MS Teams, microphone/audio fully working. So why won't it work in Zoom? (Microphone installed HP (Realtek High Definition Audio))