Flow-specific options:

• connect_account requires connection_type (card, store, or benefit_account); accepts modal.
• reconnect requires connection_id (a Sail-managed connection; external connections have no credentials and return 409 connection_not_reconnectable).
• upload_receipt accepts an optional expense_id to attach the receipt to a specific needs_review expense.
• merchant_id (only with connection_type: store) skips the vendor selection grid and opens directly to that merchant's login screen (409 conflict if the user already has a connection, active or in progress, for that merchant).
• administrator_id (only with connection_type: benefit_account) skips administrator selection and opens directly to that administrator's login screen (409 conflict if the user already has an active connection for that administrator).