The microphone volume is low.

If the microphone on your ear (1) is too quiet for others to hear you during phone calls, please try the following:
1. Check if the call recipient has the volume of their device at an audible level.
2. Ensure that you have the latest firmware installed.
3. Record audio and playback to test the microphone for any issues.
4. Check and confirm that no dirt is blocking the mics (there are 3 mics, accessed through the silver grills on each earbud).
5. Disconnect and connect the earbuds.
6. Reset the device.