I want to improve myself

Hi everyone,
I just got rejection message from Code Canyon, so I decided to post a post here to get some reviews on how to improve, here is the link to Google playstore https://play.google.com/store/apps/details?id=kadiem.app.pricetracker

A short description about the app:
The app works by adding an amazon item into watching list then the app scans for price every X minutes (defined in settings) and if there is a change in the price of an item the app sends notification

Please I’m open to any suggestion or review anything I can improve myself with.

Thanks in advance.

I think it’s about the idea, not about the coding