Hello! Could you share more information about the error? Is it a crash? You can open Console.app and inspect Safari Technology Preview crash reports to know! https://support.apple.com/en-ca/guide/console/cnsl664be99a/mac

It seems that calling LoadRequest from the mainthread fixes the issue but I don't understand why, theres no documentation to suggest this must be done. Any ideas? That's exactly right. WKWebView APIs need to be called from the main thread. This is documented on one of the WebKit API landing pages.

Please report a bug on bugs.webkit.org.

This was resolved recently: https://bugs.webkit.org/show_bug.cgi?id=261563

@mawi00, I am presented with an Apple Pay button on your website (and the payment sheet works correctly too). Are you conditionally presenting the Apple Pay button?

Hi EricMEvans! We shouldn't be showing the payment sheet after calling PaymentResponse.complete() method, since that method notifies the user agent that the user interaction is over, and causes any remaining user interface to be closed. You intend to call PaymentResponse.retry() for failures that warrant showing the payment sheet again.