When I try to install it keeps saying the package is invalid

Hmm.. that's odd? I didn't get that on my phone when I tested. Give me a second, I'll take a look. What kind of phone do you have?

I am having a similar issue on my Oangcc tablet.

It is because it is an update file not a install file like it should be. When I try to install it says 'update' as if I already have the game installed. It SHOULD say 'install'.  Also, attempting to install it via the 'update' option nets me an error 'cannot install this app on your device'. 

Edit: update on info I just figured out... So, I figured if it is giving me an 'update' option that means that it is associated with another game file; perhaps sharing a similar name for the apk. My hypothesis seems corrrct as your game has 'infected' my other game I have installed, replacing the icon of the game Mall Creeps with the icon for Bar Tapper. Whenever I open my tablet's file manager the icons fir Bar Tapper and Mall Creeps are the same, though which one it appears as changes. Originally, it showed my Mall Creeps as the Bar Tapper icon and now it is doing the opposite, if you notice.