How do ensure audio is included in live stream

I am a very new user of an ATEM Mini Pro. Twice I have failed to include the audio in a live stream from the 1 camera setup I am using. This is a simple problem of not pressing the right button on the ATEM. Please can you advise. I am using the built in mic on the camera. The camera is connected to HDMI 1 input on the ATEM. Which audio button do I need to press to ensure the audio from the camera mic is included in the live stream. To date I have pressed the Audio ON button below the extreme left mic 1 input socket. I can understand why this does not work because there is no mic input to this channel. But if the video and audio are all wrapped up together in the HDMI input to the ATEM why do I have to press an audio button ensure audio output and which button should I press. The channel 1 camera switch is lit at the time of switching on the live stream. Thank you for your help.

Press the AFV button for the channel your camera is on. AFV = Audio Follow Video, meaning that whenever your camera is used on air, it's audio is also used.

Also, you can save a default startup state where (almost) everything is set to your liking, this also includes the ON and AFV buttons for audio. Please check the manual for that.

Thank you so much eMilty. Just what I needed to know.
Suppose I add a second camera to the ATEM but when I cut to that camera I still want the audio to follow the first camera, how do I make sure that happens?

In that case you need to press the ON button on input one and nothing on the second camera. ON means that the audio will always be on, regardless if the camera is used live or not. AFV means the audio is only used when the camera is used live.