JS error in WKWebView

I received this JS error: $(".tabs li").scaleText is not a function. on this web site (https://www.topmarks.co.uk/maths-games/hit-the-button --> click "Play Game") with the WKWebView in my app.

The page works fine on Safari, chrome and even SFSafariViewController.

Could anyone please help me on that? Thank you.

JS error in WKWebView
 
 
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