Creating a sales invoice without picking or packing it.

If the sales order is already scheduled and the customer's credit has been approved, you can click the Action button then choose Create Invoice.

Since the Next Action button on a sales order can change depending on what has been done in that order, it may not necessarily be on that action you were wanting to use.  An important one that everyone uses would be creating an invoice which typically comes after all the other actions like picking or packaging.  If you want to invoice an order right away, you can click on the Action menu and choose Create Invoice to open the invoicing screen.

If you're not sure what the criteria are for the Next Action button or are unfamiliar with the use of actions on a sales order, check out this article to learn more.  Furthermore, if you often skip certain steps in the sales order process such as picking, you can disable them within Configuration Manager under Order Options.