Submits an identity you collected from a consumer for KYC verification. 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 and the resulting principal_ref. Submissions are idempotent per idempotency_key: resubmitting the same key returns the original submission instead of starting a new verification.