I’ve just noticed that audio only seems to work if the mute button (on the side of the phone) is set to loud, not mute. Otherwise there is no audio.
And yet on other audio-based websites, the audio can play with the mute button set to mute as long as the system audio (set on screen) is up. Since this is the normal across other web content, it would be the expectation of the user not to have to switch the mute button to loud in order to get audio.
Why is this happening with Playcanvas, and can it be circumvented?
That’s interesting, didn’t realise a site like YouTube can play with the mute button enabled (which seems wrong). I’m not aware of anything special that we do to have this behaviour in the engine 
Can you create an engine ticket for this please? Issues · playcanvas/engine · GitHub
Looks related: GitHub - feross/unmute-ios-audio: Enable/unmute WebAudio on iOS, even while mute switch is on
Looks like that library works with a minor tweak. See example project https://playcanvas.com/project/989428/overview/ios-force-audio
Created a ticket for this: IOS force play audio even with mute switch toggled · Issue #4678 · playcanvas/engine · GitHub