What URL does Google index if we mask the Webflow URL?

We currently have our core product built on React & hosted on AWS.

We are planning to mask the Webflow URL (website.webflow.io) via URL configuration on Nginx server, so that users will view it as www.ourcompany.com/landingpage.

In this case, what is the URL that will be reflected in Google’s indexing?

(We are concerned that Google will index the page as website.webflow.io, instead of www.ourcompany.com/landingpage)