The app allows the screen to darken if auto-lock is set in your device settings. Please set your auto-lock to never through your device settings.
iOS: Launch iOS settings, tap Display and Brightness and adjust Auto-lock to never.
1. Open Settings on your Android Phone
2. On the Settings screen, scroll down and tap on Display option located under “Device” sub-heading.
3. On the Display screen, tap on the Sleep option
Note: On Samsung Phones and some other Android devices, the sleep option will appear as Screen timeout
4. From the popup menu that appears, tap on the longest duration