Returns the fields and documents still required to complete onboarding for the selected account. Provide the level query parameter to scope the result to one verification level; a level-scoped result may also include a short-lived token for finishing the remaining checks in the embedded onboarding flow. This endpoint never runs verification — to (re-)start verification for a level, use the trigger verification endpoint and fetch missing fields again. Before a verification profile exists, a level-scoped read succeeds with empty field and document arrays; that empty pre-profile snapshot does not mean verification is complete. During any impersonation, missing fields and documents remain available, but root and country-profile onboarding tokens are neither issued nor returned; the customer must complete verification themselves.