I dont know why Epic games ignoring this feature all the time, even when we able to find a way out through VOIP and get the voicecapture data , UE4 fail to shutdown the AudioRecord() driver correctly when you close the app on android , which lead you cant recieve the input when you start the app once again unless you disable the microphone permission again manually to force reset it.
On this link you will find the solution u want . codes are included
https://answers.unrealengine.com/que…3082/view.html
while here is the bug report that epic games shifted to 4.22 instead of 4.21 .
I hope someone from epic games just give this a shot , at least anyway around .