For Android phones.
Move the slider to On
Select Mode you prefer: HIGH Accuracy
Depending on the version of the software that Android phone has, the settings would look as follows:
iOS Location Setting:
Tap on Settings and then tap on Privacy
Tap on Location Services
Make sure location is "On" and scroll down to locate the App
Depending on your iOS version you might see an additional option 'Ask'. Make sure it is set to Always.