I have attempted multiple times to call my friend in Kenya. I could hear her answer her phone, but she could not hear me. So I attempted several domestic calls and both people I called could hear me fine. Then my Kenya friend called me and we could both hear each other just fine. So I tried calling her on her other phone line and again she could not hear me, but when she called me we both could hear each other so it does not appear to be an issue with her phone. She is currently in a different part of Kenya, but I called her a few days ago and my call went through without an issue so it doesn't seem like it could be an issue with the network on her end either.
This has never happened before - I have always been able to call her. What could the issue be?