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To make a test call, select your profile picture in the top right, then Settings > Devices.
Choose Make a test call under Audio Devices.
In a test call, you’ll see how your mic, speaker, and camera are working. Follow the instructions from Test Call Bot and record a short message. The message will play back for you.
After that, you’ll get a summary of the test call, and you can go to your device settings to make changes.