Google have responded and our G Suite application is now showing in the G Suite Marketplace: https://gsuite.google.com/marketplace/app/cronofy/902414518019
It is currently offering "domain install" and "individual install". "Domain install" is the option you need to select to use Enterprise Connect.
We're continuing to correspond with Google to get our G Suite application listing accurate. It appears that they are making changes on their side at the moment.
The published link of https://chrome.google.com/webstore/detail/cronofy/addpjfjiamildabdcppfadfmiloppkhl
redirects to the G Suite Marketplace listing and so should still work. We will be updating our site and documentation to link directly to the G Suite Marketplace once we have confirmation from Google that all issues are resolved.