One-way audio from customers?

If an agent can hear the customer, but the customer can't hear the agent, this may be the result of an application taking exclusive control of agent's mic/speaker.

You can search the internet for articles that explain how to turn off exclusive-mode for a Windows audio playback device. For example, Turning off Exclusive Mode in Windows 10 Home Edition.

To fix sound problems on a Mac, see Change the sound input settings on Mac.