Multiple domain names
As it is not recommended to use more than one domain for a website, you can only configure one custom domain at the same time.
If needed, it is possible to update the custom domain, but the previous domain name will be removed.
If, for any reason, you need to have your website accessible from multiple domain names, you can create redirections from your Registrar Dashboard (where you have bought your domain name). This way, you won't have duplicate contents issues with search engines.