itch.io

Hey, may you try to do this:

Before you click on download, go to the 3 points at the right top of your browser, then search the option  "desktop site" this will change the whole page as you were using in a PC, them try to download again.
Like this> Change to desktop mode on your mobile browser

And if this don't work, try to turn on the option "download from unknown source". 

Like this> How to Install Apps from Unknown Sources in Android