Upload Session Document

Upload a document image to a session.

Supports id_front, id_back, selfie, and proof_of_address document types. Replaces any existing document of the same type (idempotent). If the session was in pending status, transitions it to capturing.

For proof_of_address uploads, the optional poa_document_type, poa_document_date, and poa_issuing_country form fields store classification metadata on the session — the same fields the web capture flow collects.