The Event App is a simple web app you can add to your home screen instead of downlaoding from the app store. To install the web app, scan the QR Code, or go to https://waisa.org/pwa. When you have opened the Web App, you must add it to your Home screen before it will run. 

For Android and iPhone, click the share icon -> Add to Home screen. On Android you might see three little dots at the top of your screen. Next, open the App from your Home screen and enable notifcations.

Sometimes, depending on the phone and OS, Home screen might be locked. If you cant add to the home screen, try checking Settings > Home Screen and ensure "Lock home screen layout" is off.

Note: If the app stops working for any reasons, just delete from the home screen and add it back again.