If you'd like to delete an invoice forever, here's how:

1. Go to the Invoices page and find the invoice you'd like to delete.
2. Click on the three vertical dots to open the menu and click on Delete.

Alternatively,

1. Click on the Menu icon and go to the Clients page.
2. Find your client and click on the Invoices tab.
3. Find the invoice you'd like to delete, click on the three vertical dots to open the menu, and then click on Delete.