Sorry, I was wrong before when I thought the issue was fixed by me updating iOS. That was just a coincidence. It looks like the real issue is that you can only listen to outside audio if you start the audio while the Siralim app is completely closed. If you have the Siralim app open, then go to the home screen and open the audio, and then open the Siralim app again, then it doesn’t work. Siralim stops the outside audio and plays its native audio.
To make it work, you have to completely close the Siralim app in the task manager (double tap the home button to open the task manager, then swipe the Siralim window off screen) and then start the audio and then open Siralim again. Note that this makes you lose any progress you had in the current realm you were in, so wait until you finish a realm and make sure to save before you close Siralim.
I think I’ve used other apps that didn’t require the app to be closed in the task manager for outside audio to play. If you can make Siralim do that too, it would be great. It confused me trying to figure out how to make it work and I’m sure it has confused or will confuse some other people too.