Yes, an invoice issued may be changed if:

– you have not already sent it to the client or

– after you have sent it, the client asks you to change the invoice (only if it is not already entered in the accounting)

If one of the two conditions is not satisfied then better:

– cancel the invoice or

–  totally or partially reverse it

*Important* : be careful if you delete an invoice because you can interrupt the sequencing of the numbering and you will have discontinuity in invoices; which could cause you problems with the Financial Administration.