During a Video Call, I can see and hear my contact, but they cannot see or hear me.

Check to ensure that your media settings and device permissions are set correctly, then try your call again.

If you are certain your internet connection/WiFi signal is good, please try the following:
1. Open your Account Menu (top-left corner of the home screen of the app. 
2. Scroll down to see the Media Settings section
3. Ensure your Audio and Video sources are correct.
Normally, it will display the default settings of the device used, but you may want to try selecting different options if you are experiencing issues and try your call again.