Why subdomain over root domain
No risk to your main site — a subdomain A record is entirely separate from the root domain's DNS. If anything goes wrong, your www stays untouched.
Multiple campaigns — run quote.yourbrand.com, book.yourbrand.com, and refer.yourbrand.com each pointing to a different form, all under the same brand.
Easy rollback — if you ever move away, removing a single A record scopes the change to just that subdomain.
Setting it up
In Connect → Deploy, enter your full subdomain — for example, quote.yourbrand.com.
In your registrar's DNS panel, add an A record with the host set to just the subdomain part (e.g. quote) pointing to 216.150.1.1.
Add the TXT verification record(s) shown in the DNS table.
Click Refresh in Connect → Deploy to check verification.