PK4 TimeTracker is an online app. That means you need to be connected to the Internet, either through Wifi or through your device's mobile data. If you are not connected to the Internet, you may see a blank screen, when you log in to the PK4 TimeTracker application on your mobile phone.
Please make sure that you are connected to the Internet and then re-login to the PK4 TimeTracker application.
We suggest you login to the PK4 TimeTracker application with a good data or Wifi connection. Once the app is synced with proper data connection you can Check-In/Out for Job/Project even if there is no data connection on the device.
All the Check-In/Outs done when offline gets posted to Salesforce once the device is connected with proper data or wifi connection.