Returns share_url, the client's view link for this invoice, and the full document (parties, lines, totals in integer CENTS) in one call. action: 'get' (default) returns the live link; 'rotate' replaces it and the old link stops working; 'revoke' turns it off. A link the owner turned off stays off for agents: 'get' never re-issues it, and an agent's 'rotate' waits for the owner's approval. Anyone with the link can open the page until the invoice is cancelled or 90 days after payment (see link_serving). There is no PDF file yet; the link opens a print-ready page the client can print or save as PDF. Nothing is sent: give the link to the owner, who decides whether it goes to the client.