Can anyone please explain to me how the CLONE FEATURE works?
On already created sales invoice, click view then click Clone, that makes a clone/copy to save you entering the same data twice, click create. Simple. Give it a try.
It also works on other forms when clone button is visible.
Remember that cloning only populates a transaction screen. In most cases, you will need to edit the transaction. And you always need to Update so the transaction is created.