HTML5 Stereo Sound Issue in UE4-23

Hi I have a question about sound in HTML5.
I am exporting my scene to HTML5 in UE4.23.1. I have a spatial sound in the scene so that I can hear the sound panning when the character is facing different directions.
However when I launch it in web browser, the panning stereo sound is not there though I can hear the volume change up/down when get closer/farther to the sound source.
Changing directions wouldn’t affect the sound.
Anyone know why? Thank you very much in advance!