“Why won't this order invoice correctly?” is not one problem.
Start With the Order Type and Status
A standard order, master order, repeating order, quote, backorder, or other workflow does not necessarily behave the same way.
Check What Has Actually Been Shipped or Selected
Quantity, backorder, shipment, warehouse, item status, and fulfillment activity can all affect what reaches the invoice process.
Then Check the Surrounding Rules
Pricing, tax, freight, ship-to, customer setup, forms, and integrations can change the result even when the line item itself looks ordinary.
Do Not Troubleshoot From a Blank Test Order Too Soon
The problem order contains history.
We want to understand what happened to that transaction before creating a cleaner example that may accidentally remove the exact condition causing the issue.
Follow the Order Into AR
If the invoice posted but the customer or financial result looks wrong, the investigation continues into Accounts Receivable and the General Ledger.
Sales Order is one point in the transaction lifecycle—not the end of it.