First, make sure you have installed node.js 10.X and npm 6.X version. You can check it on own terminal window by merely entering node -v and npm -v . You can also download latest nodeJs from here
$ npm -v //version will be 6.X$ node -v //Version need to be 10.X max .
once node and npm install on your machine, we need to install Ionic globally as well.
// You can install ionic globally on your machine with below command$ npm install -g ionic$ npm install -g cordova
Ionic is recently doing lots of changes with ionic V4 and default if it installs ionic-cli V4 which might break few things if you still running our ionic V3. Most probably their app-script module needs to update with the latest one then this app run correctly with ionic cli V4 as well.
You can get V4 update version from our website IONIC FIREBASE MOBILE APP V4
Make sure you have installed ionic-cli latest release and Cordova. You can check ionic version in the terminal with ionic -v command. If you need more info how to setup ionic project please follow Ionic Getting Started at Ionic official websites.
You need XCODE AND Android Studio to make production build that can upload on app store.
We suggest to use ionic pro to make native build easier as setup through Xcode and android studio bit difficult if you new on app development.