(I work at Cloudflare). You can sign up just a subdomain (sub.foo.xyz) as an enterprise customer and then add an NS records from your DNS provider to Cloudflare

(I work at Cloudflare). You can sign up just a subdomain (sub.foo.xyz) as an enterprise customer and then add an NS records from your DNS provider to Cloudflare for that subdomain. Tunnels also has a testing domain you can use. It should give you a subdomain like xxx-xxx-xxx.trycloudflare.com for basic "How do I get this thing working" testing.