I'm sorry, Android can be very finicky. Are you sure you have enough space on your phone? Other renpy games work without issue?
I had to double check but yes I made sure I had enough space on my phone, and I tried to update a few other renpy games that I have on here as well and those seem to work as well. this is the first time I've ran into this issue, and it doesn't give me any reason as to why it won't proceed with the update. My webpage does display a "file might be harmful" warning message before it starts the download, and while it has done that for a few other games I THINK this is the first time it's done it for Greener Pastures.
Edit: I tried updating the game from the hotbar in my web browser and it popped up the message in the image attached. I still have no idea what this means, but I hope it helps resolve it. 