If you look in the source of your page, it looks like that is what is being attempted. There is a script for communicating to the Customizer endpoint about preview-0
.
It also says that the page was optimized by KingComposer Page Builder, whatever that is or does (not sure if that is affecting it).
I would first try it without the KingComposer. But I’m not sure how to get out of the clutches of the Customizer if you didn’t even intend to be in it.
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