Set the domain's contacts. registrant is required and replaces the current registrant in full; admin, tech and billing are each left untouched if you omit them. Registries validate registrant changes, and some TLDs require extra fieldson the registrant (for example ca_legal_type for .ca). A rejection comes back as 400 with the registry's reason in extra. Some TLDs alsotreat a registrant change as a trade requiring approval, so the change maynot be visible immediately. Responds 200 with no body.