No, it is not necessary.
Your steps are counted by your phone or connected device even if the Kiplin app is closed and location sharing is not enabled.
You do not need an internet connection to count your steps.
However, you do need to be connected to the internet to synchronise your activity. When you open the Kiplin app, your steps are synchronised and appear a few moments later.
Best practice: open your Kiplin app at least once a day to synchronise your data.