StepsApp stopped counting steps

Please update to the latest version of StepsApp.

Update iOS

Open Settings on your iPhone
Go to General
Go to Software Update

Check Motion Sensor setup

Open Settings on your iPhone
Go to Privacy
Go to Motion & Fitness
Enable access for Health and StepsApp

Check Apple Health setup

Open the Health app on your iPhone
Tap on your avatar in the top right corner
Go to Apps
Go to StepsApp
Enable all switches

In some cases it also helps to restart your phone.