How to copy opportunity items as sales order items

Go to Sales & Marketing > Opportunities.
Select the opportunity.
In the opportunity items category, select the opportunity items you want to copy using the check boxes.
Click Copy to existing sales order and click ok in the dialog box.
Sales order form opens.
Sales order form shows the created items and you can edit them.
Click Save.

You have the required access right. (CRM > Opportunites > Opportunity copy items to sales order)
The opportunity and the Sales order point to the same project and opportunity’s contact is the same as project’s contact.
The sales order is in ordered status.
The opportunity has opportunity items.