Wix Headless provides you with the flexibility to create an app or site on any platform and take advantage of Wix's business solutions via APIs. However, for some processes, such as authentication and checkout, you can save time and effort by using standard pages Wix implements for you. These Wix-managed pages are incorporated into the flow of your external site.
If you use Wix-managed pages for processes such as login and checkout, the Wix pages domain will be the domain visitors see when going to those pages.
To set your Wix pages domain:
In your project dashboard go to Settings > Headless Settings.
On the Headless Settings page, scroll down to the Manage URLs section.
In the Wix pages domain section, you can view your free Wix domain, and you can customize the path that visitors see. For example, if your free Wix domain is http://sandrasworld.wixsite.com/ and you enter the path my-project, visitors are taken to http://sandrasworld.wixsite.com/my-project.
If you've purchased a premium plan, click custom domain to connect a unique web address you like, instead of your free Wix domain. Follow the instructions to either connect a domain you already own or purchase a new domain.
You may wish to connect a subdomain of your external site's domain, to make visitors' experience seamless. For example, if your external site is at my-external-site.com, you can make portal.my-external-site.com the URL that visitors see when they are redirected to a Wix-managed page. (Note: You can connect a subdomain of your external site's domain, but you can't connect your external site's domain itself.)