entityKey is used after you convert them to Active clients. Deals are a separate pipeline object with their own statuses and sources.
Settings first
Create a lead
Write access required.POST /api/v1/leads.
Individuals / sole traders: entityName = given name, entitySurname = family name (not auto-split).
Companies: entityName = legal or trading name; leave surname unset.
Convert to client
entityKey does not change. 400 if the entity is already a client.