Creates a new Account under the given parent. Provisions the container that holds a customer's money, KYB, and tax artifacts before any other resource is attached. Principal and authorized-representative data are added separately through Stakeholder records: the Principal with isPrincipal=true, the authorized representative with isController=true. The creator receives Admin access. No Principal is assigned at creation. A business of one (a sole proprietorship, a single-member LLC, or a single-owner S-corporation) sets its Principal with POST /platform/accounts/{accountId}/transfer-principal, or by creating a Stakeholder for the Person who becomes Principal with isPrincipal=true; a business with more than one owner has no Principal. ServiceAccount API keys and Account sessions minted by ServiceAccounts can create children only: parentAccountId is required, and the ServiceAccount needs live Write authority on that parent that extends to new child Accounts, plus users.account:write permission. API keys must send X-Wingspan-Account. Account sessions must include descendants, and the parent must be the bound Account or one of its descendants; their header is optional and defaults to the bound Account, or may select a descendant. These sessions inherit the minting key's scopes; the mint request cannot narrow them. To mint embedded sessions without child-create permission, use a key without users.account:write. Person callers MUST NOT send X-Wingspan-Account. Account-bound Person sessions, leaf Account sessions, and impersonation-issued sessions cannot create new Accounts. Idempotency-Key replay is partitioned by the effective Account whenever one exists, and by the authenticated Person only for unbound, headerless Person callers. The shared response cache may replay a stored response without executing a new create.

If externalId is supplied and already used by another resource of this type for the owning Account, the request returns 409 ResourceConflict; create is not an upsert. Use filter[externalId][eq] on the list endpoint to retrieve the existing resource.