Issue Po Invoice

Issue a pre-payment invoice for a Purchase Order.

When a customer pays by PO, the business needs to send them an invoice BEFORE payment arrives so their AP team can cut the check. This endpoint generates the invoice (status=ISSUED) without touching the payment's status or the project's state. The customer will see the invoice in their dashboard and can forward to AP. When payment later arrives, mark-received flips the same invoice to PAID.

exclude_tax=true renders the invoice tax-free (e.g. tax-exempt org, or tax accidentally added to the quote) without touching the quote.

Optional additional_line_items_post_tax (request body) adds admin-entered post-tax extras (shipping, …) to the invoice — billed beyond the quote, summed into the total after tax, quote untouched.

acknowledge_total_drift=true bypasses the reconciliation gate below. Use it when the recorded settlement genuinely differs from the quote (the normal case for a MANUAL out-of-band payment); leave it false so a stale quote.total_amount can never silently become a bill.

Gates: PO method, payment PENDING, PO number submitted, no invoice already issued, recorded amount reconciles with the quote (400 quote_total_drift otherwise). Requires payments:edit permission.