First, verify the source being sent to Virtual Input. Next, go into your Outputs/NDI/SRT settings in vMix and click the Gear next to the Output you are sending to Virtual Input. This is where you select the audio signal being sent on the NDI Output. Make sure you are sending the correct Audio Channels that you wish to send. You can send a number of different audio signals on each NDI output (Master, Bus, both). If sending Master, verify the correct sources are going to the Master. If you are sending a Bus Output make sure the correct sources are going to that Bus and that the speaker button on that Bus is green. Also note that you can route audio out of vMix on any Bus without that Bus being sent to the Master.

Are you getting a signal from all of your audio sources on the Master/Bus Audio Meters?

Something else you could test is instead of sending Master Audio to teams assign the audio sources you want to send to Teams to a single Mix Bus (A,B,C,D, etc.) then go to your Audio Outputs in the Settings. Next to Headphones, select None from the dropdown menu. Next, find the Bus you want to send to teams and select Speaker/Headphones from the Dropdown menu. Exit the settings and play the audio you wish to send to teams. If you can’t hear it in your speakers/headphones then it isn’t being sent to the Bus correctly. If you can hear it, and the correct Bus is selected in the Output/NDI settings, your problem isn’t in vMix. Note that when you finish this test be sure to change the Bus back to Enabled (or whatever it was on before) in the Audio Outputs.