Are you on the app store?

The GigPay wallet is what's called a "Progressive Web Application", aka PWA.

For an overview on this check out https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps and
https://virtualspirit.me/insights/136/is-the-progressive-web-app-pwa-still-relevant-in-2023

In short, think of it as a portable browser webpage (Chrome, Safari, Brave, etc). Not as a "go to the App Store, search, download, install and set-up". 

For more info on how to add the progressive web application to your phone, please visit: How do I add the Gigpay wallet to my phone?