I can't download on android because it's not for the latest version
I had the same message for the free version, It had said something along the lines of "this app is unsafe because it runs on an old version of Android" then there was a button that said download anyway hidden. I was able to download it though.
Also very nice game so far! I got to the plant and then bought the sub for the access to the scene. I really enjoy the exploration so far and the customization!