This is not a hack or bug, this only a simple audio format. this is for message tone not ringtone.
I discover this since i explore my default message tone on my phone and i saw the “facebook pop” tone and when i checking my internal storage file and find the facebook pop file. i check the file format its not a mp3, it’s a m4a format. so you need to convert your audio if you want a custom message tone on your phone.
Android : m4a ( that whats i know, you can try another format if you want. except “ogg, wav,”) for samsung. For asus you can use mp3 make sure that you put your mp3 file on notification folder in internal storage. I didn’t test to other phone so you may try it and error if you want.
IOS/ Iphone / Ipad: m4r ( I’m not a apple user i saw this format on google.)
that will be the format. “you must put your audio file on your internal storage (any folder you want)”