Create a Salesforce lead by email, or return the existing one. company_name is the lead's company ('[not provided]' when missing, as Salesforce's own web-to-lead). first_name/last_name are sent as given; full_name is split only when both are missing. Salesforce requires a last name: without one the create is a bad_input miss.
Price: $0.00 per unit.
Maximum charge per unit: $0.00.