Web App Install Banners - Error

Hi Guys, I am new to progressive web app, I am planning to convert one of my projects to a progressive one but when I tried to test adding a Web App Install Banners which I followed the documentation here https://developers.google.com/web/fundamentals/engage-and-retain/app-install-banners/#testing-the-app-install-banner I got this error
_**Site cannot be installed: no matching service worker detected. You may need to reload the page, or check that the service worker for the current page also controls the start URL from the manifest**_
This is the link of my site, hope you can help me
https://fundraising.avalonpearls.com/

Thanks in advance