If the sales order is related to a project or a WBS project, you can make this relationship under the "Accounting" tab -> "Project" tab of the sales order.
For this, you need to select Project from the "Projects" window, and if you later want to define a WBS Project , you can select it from the "Project Tasks" window. By saving and sending them, you can link them to the document.
If you want to associate more projects, after selecting the first one, you should write "% Rate" and save. The system will show another two-row field to add more "Projects" and "WBS Elements" and will show the remaining % rate that completes 100%.
To delete project records, you must check the "Delete" checkbox and click the "Delete" button.