Okay! I think I know the reason. This site is hosted on
www.Heroku.com which is a PaaS provider. I am using its free plan to host the API. So, my app is hosted in herokuapp.com (
https://minee.herokuapp.com). Since it belongs to the domain `herokuapp.com` and since a lot of people use it, I think the root domain `herokuapp.com` itself is shown as a Malicious site. The problem will be solved once I get cash to move the app to its own domain.
Thanks a lot for the info

And thanks noel57 and coinableS. Will keep posted in this thread.
All right, i see.
maybe i will use it for my site.