Deliver the invoice document to the policyholder, gated on an invoice_sent notification template being configured for the organization and the policy's product module.
Sending is repeatable and does not change the invoice's status. An invoice can be re-delivered as often as needed, at any status.
When no template is configured the call still succeeds with 200 and returns { "sent": false, "reason": "no_template" } rather than an error, so that a caller can fall back to downloading document_file_id and delivering it manually.
Invoicing is opt-in per organization: unless the invoicing feature flag is enabled for your organization this endpoint returns 403.
The invoice has no rendered document to send.
Invoicing is not enabled for the organization, or the caller is missing the invoices:send permission.
No such invoice, or the caller's user group does not grant access to its policy.