Moon Invoice users can delete the Task or the Project which are complete tasks or which are no longer needed. Project/ Task which was previously used in any of the Invoices can only be Archived to hide it from the list. 

Please follow the steps to delete Project/Task;

1. Go to Project from the left panel.
2. Click on the edit button at the top panel.
3. Select the Project/Task which you want to delete and click on the delete button. 

For reference please check the screenshot; 

- Moon Invoice