Don't use root domain for instance.

main.tf

@@ -104,7 +104,7 @@ resource "digitalocean_reserved_ip" "machine" {
 
 resource "cloudflare_dns_record" "root" {
   zone_id = var.cloudflare_zone_id
-  name    = "@"
+  name    = "_nassella-instance"
   content   = digitalocean_reserved_ip.machine.ip_address
   type    = "A"
   proxied = false
@@ -115,7 +115,7 @@ resource "cloudflare_dns_record" "subdomains" {
   for_each  = toset(var.subdomains)
   zone_id = var.cloudflare_zone_id
   name    = each.key
-  content   = var.domain
+  content   = "_nassella-instance.${var.domain}"
   type    = "CNAME"
   proxied = false
   ttl = 300