Configuring a custom domain for your status page is easy with Fluid Status, you just need to go to click on Custom Domains in the sidebar of your dashboard and click on Connect custom domain, a new section will appear:
The domain/sub domain you enter in the text box can be anything you want as long as you own it and have access to its DNS settings, before you proceed to enter the custom domain and save the settings you should follow these steps:
Create a CNAME record in your DNS management tools that points your desired domain (in the above example status.yourcompany.com) to fluidstatus.com (literal string).
If you use CloudFlare as your DNS manager make sure to set it to DNS only for this domain.
After configuring the CNAME record you might have to wait a few minutes (even hours sometimes) for it to propagate, you can verify if it's already propagated with a tool like DNS Checker.
After following all the steps above you can enter your custom domain in the text box and click on Create.