Strangely, if you kick it back into sandbox mode it will let you complete just fine but if you put it in live, it just progresses to checkout_confirmation without the prompt and then falls back to checkout payment with a payment auth error. So weird.

I've been going around in circles trying to get this to work because it works in sandbox but not live, but in a weird way it's nice to know it's not just me.

In sandbox, if you use open the browser console as you progress throuch checkout payment, you can see the request to squre for the SCA modal, but in live it doesn't. Thsi was working up until yesterday morning.