Request body schema for creating an account (POST /accounts).
Extends the shared Account schema with the create-time contract: the fields the API requires on creation are listed in required, and each of those that is nullable in the response schema is re-declared here with their nullable state, since a required field that is non-nullable cannot be sent as null. The response representation keeps Account (where these fields may legitimately be null for legacy/partial accounts).
To create an office (organisational unit), include parent_id in the request. The parent must be a top-level account within the same group — it cannot itself be an office. When parent_id is set, tin_value and tin_scheme are inherited from the parent and must not be provided.