Huawei phones have a custom energy saver mechanism that makes them behave differently compared to other Android based smartphones.
In order for Toky (and other VoIP apps) to work properly, you need to enable it as "protected app" so that the operating system doesn't stop the app as soon as the screen goes off or when your phone enters Sleep Mode.
To accomplish this task please follow the following steps:
1. Go to "Settings"
2. Select "Protected apps"
3. Find Toky, and turn it on