Sony LinkBuds S YY2950 Reference Manual page 89

When Service Link is turned on and only the left unit is worn in your ear, the Speak-to-Chat mode will not be activated even if the
headset detects the wearer's voice.
If the sound volume is loud, the headset is not worn properly, or the volume of the spoken voice is low, the speech of the person
wearing the headset may not be detected, and the Speak-to-Chat mode may not activate.
If this is the case, speech detection may be improved by speaking more slowly or in a louder voice, making sure the headset is in
the correct position, turning down any music playing, or setting Speak-to-Chat to "H Sensitivity".
Related Topic
What you can do with the "Sony | Headphones Connect" app
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