By default, when projects is enabled it allows you to attach entire invoices and purchases to a project. This guidance advises on how to instead attach individual line items to a project.
To set your projects at line level, go to Settings > Project Settings > Tick ‘Let me assign individual lines of Invoices to different Projects/same for purchases as required > Save Settings.
Assign to Invoice Lines
Assign to a line item on an invoice by going to Invoices > Select the invoice > Click Edit > Select the project using the drop down on the line item> Save.
Assign new line items to a project by clicking the Add Line Item button > Use the project drop down to select the project to attach this to > Save.
Assign to Purchase
Existing Purchase Receipt
Assign to a line item on an receipt by going to Purchases > Select the Purchase > Click Edit next to the line item > Select the project using the drop down > Save.
New Purchase Receipt
Assign new line items to a receipt by clicking the Project drop down to select the project to attach this to > Proceed to create the line item.
Note: Enabling this would not allow you to show the Project name on the invoice PDF.