Submits a consumer identity together with the business they operate for KYC + KYB verification and evaluation of the operator link between them. Verification runs asynchronously: the request is accepted with a 202 and a submission id — poll GET /identity-submissions/{submission_id} or subscribe to the OnboardingSession.completed webhook for the outcome, the principal_ref, and the business_ref. Submissions are idempotent per idempotency_key.