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You will only be able to Re-Invoice if a Credit Note has been raised against the original Sales Invoice. If this is not the case, you will not see that as an active option.
When you select to Re-Invoice a Sales Order a pop-up message will appear to explain you are about to create a copy of the invoice and a New Invoice. You will be able to edit this invoice and it will be in the same project you were working in.
You will not be able to delete the original invoice and credit note on the project, you can only cancel the documents.