Before your mapped domains will work, you'll need to ensure that both your DNS records and server settings are configured properly.
Your DNS records should be configured the same as a normal website. Point the A records of any domains you want to map to your WordPress site's server.
We recommend using CloudFlare as your DNS host, but you can manage DNS records at your domain registrar or any other CDN or DNS provider you want.
Here are instructions from Cloudflare on how to set up DNS records properly.
Here's a video we made about setting up Cloudflare for your website.
If you aren't sure how to set up or manage your DNS, please submit a ticket and we are glad to help.