Why can´t I seem to find the Enter/Update function on the SO screen?

Once a Sales Order has been created, and you have the necessary permission to invoice customers, the Enter/Update option will appear under the three-dot menu on the right side of your screen. 

If this option does not appear, one of the most common causes is that the Proforma Invoice checkbox is selected. To resolve this, simply edit the Sales Order and uncheck the box. Once updated, the Enter/Update option will become available.