Why does my invoice show a negative-stock warning?

This warning appears when an invoice line item would take a product's stock quantity below zero — for example, invoicing 20 units of a product that only has 15 recorded in stock.

To resolve it:

1. Check whether a recent purchase or restock needs to be entered first.
2. Check whether the product was sold through another channel (POS, in-store) and hasn't been recorded yet.
3. If stock is genuinely correct and the sale is intentional (for example, a pre-order), you can proceed — the invoice will still save, but the product will show a negative-stock flag in Inventory until it's corrected.

See Understanding negative-stock flags in the Inventory help category for more detail.