In the Web app
There are two ways to close sales orders in the Web app:
Option 1. Go to Sales → Sales Transactions, locate the sales order you want to close, click its reference number, then Options
and select Close.
Option 2. Go to Sales → Sales Transactions and find the sales order you would like to close. Select Close in the Actions column.

You can also partially close a sales order manually by checking the
Closed checkbox in the sales order item lines on the
Edit Sales Order window. See also
Reviewing Sales Orders in the Web App.

Closed sales orders cannot be edited,
picked and packed, or
invoiced but they can be re-opened by doing exactly what is described above but selecting
Open instead.

On the Mobile Device
Go to Sales → Customers → tap the necessary customer, then tap Sales Orders in the pop-up window. In the Sales Orders screen, select the necessary order(s) and tap Invoice in the bottom-right corner of the screen.
Once you’ve found the desired sales order, you can edit it by tapping the order and then Edit.
You can manually close the order by tapping the order in the list and tapping Close in the pop-up window.