There are certain two ways to make sales invoice, either you can make sales invoice from the sales order or by converting quotation into sales invoice, First if you make sales invoice from sales order, click on the “Task” from the menu bar and select the option of “Sales/Invoicing” from drop down menu like below After clicking on sales/invoice the following window will appear.. In that window you can see that, there is only one tab is active that is “Apply to sales”, you have to select the customer ID to whom you want to make sales invoice,as you select the customer Id the first tab “Apply to sales order” will activated as shown below In this window you can see that there is option in front of “Apply to sales order”, in this option you will have to select the number by clicking on down arrow button like below By clicking on that the following screen will appear In this screen you will only have to give the number of units which you want to ship and give the invoice number,that