When shipping some (or all) of the items on an Order, the Order and the new Invoice have the same transaction number. After the shipped items transaction is saved, both the Order and the Invoice now also have a letter following the transaction number.
For example, for a Sales Order with the transaction number 123:
Nothing Shipped - No Invoice exists - Sales Order 123
Everything Shipped - No Order exists (or Order exists with no qtys) - Sales Invoice 123A
Partial Shipment - both Order and Invoice exist - both are 123A
Second Partial Shipment - both Order and new Invoice exist - both are 123B
In the above example, the first Order is still 123A and each new Order/Invoice is lettered consecutively.
Note: If an order is converted to an Invoice using [Shift]+[F9] (creating a Back-ordered Invoice), the new Invoice does not have a letter. If it is a Back Order, new invoices are not be created each time it is partially filled.
Sales Transaction - Number
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