Create a sender ("from") email address. Provide username and name (the from-name shown on emails). By default, the address is created on ClickFunnels' shared sending domain. To use a custom domain, first provision it with POST /workspaces/{workspace_id}/emails/domains, add the returned DNS records, and have the customer connect that same root domain to this workspace as a website/hosting domain in the ClickFunnels app. Both halves are required and no API call can do the second one, so DNS records alone never make a domain ready. Re-check with POST /emails/domains/{id}/verify until ready_for_sending is true, then pass the domain's numeric id as emails_domain_id. An address created before the domain is ready is allowed; it simply reports usable_as_sender: false until then. See Addresses (pick a usable sender) in the Emails Skill.