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.