In most cases, background audio should work (both in the background and in the lock screen) without any modification on the site itself. For iOS, please activate background audio in the Xcode project: https://www.webviewgold.com/docs/iOS/#audio_background 🙂
From our investigation, it appears that setting silent mode on iOS devices can now block WKWebView, while standard web pages (and specific other applications) can continue to play sounds. Please unmute your device. This behavior seems to be an issue on iOS 13.3.1 (and above). There is an official bug report to Apple (this bug is relevant for ALL WebView solutions, not just WebViewGold): https://bugs.webkit.org/show_bug.cgi?id=204261
Hopefully, this problem will be fixed by Apple with an upcoming iOS release soon.