Memrise on Iphone can not hear audio

Memrise Bug Control iOS Bugs
1

Hello.
I add audio to my course.
But iOS can not display audio.
This error with Memrise 2.3.26
Thnaks

2

My course: https://www.memrise.com/course/1944701/tieng-nauy-thuc-hanh/

I use app Memrise on Iphone and dowload course. But course er display only text, can not hear audio. (but I can hear audio on website)
Thanks