There is no built-in mic for RLC-423/RLC-423S/RLC-423WS, so if you'd like to get audio, you need to install an external microphone for RLC-423/RLC-423S/RLC-423WS.
You may follow the article below to install the microphone for RLC-423 series cameras.
How to Choose Microphone for RLC-423/RLC-423S/RLC-423WS
How to Install the Microphone for RLC-423/RLC-423S/RLC-423WS
And you could follow the article below to enable audio on RLC-423/RLC-423S/RLC-423WS.
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