Creates a Stakeholder record. One Stakeholder per (subjectType, subjectId, accountId) triple — duplicates return 409 ResourceConflict. For Account-typed members, roleId, roleIds and scopes must be null (Account-to-Account access flows through parentAccountId hierarchy and Organization policy controls). An Active Person without acceptance returns 409 with users.StakeholderAcceptanceRequired; create the teammate entry by email, invite it, and ask the Person to accept from their own session.

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.
isPrincipal=true, unresolved natural-human Stakeholders (subjectId omitted), email-only Stakeholders, and subject-bearing accountSuppliedComplianceEntityId attachment are backed by the users service. Because Stakeholder ids are normally server-assigned, external clients usually create the Stakeholder first, create the subject ComplianceEntity with the returned id, then PATCH this field.

Requires a session with recent MFA step-up for StakeholderChange. If step-up is missing or expired, this operation returns 403 StepUpMfaRequired; create and verify an MFA challenge at /v3/platform/mfa-challenges with requiredFor: "StakeholderChange", then retry.