Looks like a problem on their end. They may have signed the newer version with a different key from the older version. So Android refuses to install it. I really don’t think Mitch has any influence over this, but I guess you could try downloading and installing the new APK manually. If that doesn’t work your options are 1) complain to game dev or 2) delete the old version (which might erase the save data!) before installing the new one