Finding a bug and repairing the Application, English Kotlin program

A company has created an application on my behalf. The application was to remind you to water the plants, but from

At the beginning there was a problem, the application stopped sending the watering message after a few days, despite the fact that the application clock was working fine. A friend of the programmer looked at the application and found that the source code is ok, according to him the problem may be communication between the application and the operating system. Unfortunately, Kotlin's friend knows it superficially. The application was written for Android.

I need someone to find the bug and fix it.

The downloadable app on the Google Store is called Waterizo:

https://play.google.com/store/apps/details?id=pl.korizo.waterizo