Your location isn't updating correctly? Maybe your friends only see your real-time location when you have the app open?
If so, there's a good chance that battery-saving settings are enabled on your device. These settings can prevent Zenly from running correctly in the background. Therefore, your friends will only see your real-time position when you have the app open.
Please troubleshoot the following steps to ensure that battery-saving settings are disabled:
Android 5.1.1
Battery > Power saving mode / Ultra power-saving mode
Battery > App optimisation: Detail > ON / Zenly > Disabled 
Android 6
Settings > Power saving > Power saving mode / Ultra power saving mode
Settings > Battery > Detail > Zenly > App power saving: Turned off
Android 7, Android 8, Android 9, Android 10
Settings > Device maintenance > Battery > Unmonitored apps > Add apps > Zenly
If the above steps do not resolve your issue, please consult the article, "My location isn't updating – Android" for further help.