Customer document numbering is sequential and continues this way based on the numbering that was originally setup when the company was created. It is possible to change or reset the numbering for Orders, Invoices, Goods Received Notes and Credit Adjustment Notes in the Customer Invoicing options.
Go to Setups, Customers, Options, Invoicing Options.
Find the Next Document number section.
Set the next Order Number, Invoice Number, Goods Received Note or Credit Adj Note Number as required for any of the fields. The fields are 6 digits long and you can use numeric or alphanumeric numbering.
The number entered will be the next number used.