Returns a link to download a PDF statement for the user's Bakkt bank account. Supports a flexible period via date_from and date_to (YYYY-MM-DD), max 366 days. Once generated, the statement is an immutable snapshot. Returns HTTP 501 when statements are not enabled for this environment; otherwise returns 200 with { url }. Omit dates to use the default period when supported. Merchant/API key with user_uuid in path.