How To Fix Telegram Suddenly Lost Input Sound on KDE

Recently I got an issue on Telegram that I suddenly could not speak to my voice call students on my computer with my favorite Plasma Desktop. This issue blocked all my teaching sessions since mid May and I was forced to use another (fortunately I have) operating systems with Telegram in my computer without Plasma which is less convenient for me for this job. Fortunately now after doing a workaround in volume control, it is solved, and finally I can do my job again. If you encountered similar issue with other software like Sound Recorder or Audio Editor, you can use this report too to solve it. Here is my report.

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• KDE neon 5.13 operating system, equal to Kubuntu 16.04.
• Plasma 5.13 desktop environment.
• Telegram Desktop.
• PulseAudio Volume Control installed. 
• Samsung cheap cable headset as input/output device

• Open Telegram Desktop.
• Click a friend.
• Click telephone button.
• A voice call ringing.
• Friend accepts call.
• I speak to him, he speaks to me.
• I can hear him, but he cannot hear me.

• When voice call goes inactive, volume control does not display controls over input choices. 
• The two choices "Monitor..." and "Built-in..." do not appear on desktop system tray.
• Some other software also suffer same issue, namely GNOME Sound Recorder and Audacity, but others work normally, namely Kazam and Jitsi.
• Telegram on other operating systems work normally without this issue.

• Open PulseAudio Volume Control.
• Do reproduce steps above.
• See volume control in the Recording tab.
• Change input choice from "Monitor..." into "Built-in...".
• I can speak and other party now hears my voice.
• Problem solved.

(Correct configuration in pavucontrol)