It is usually a bad practice to alter an invoice after it has been issued but can sometimes be needed.
What can be edited
If QuoteMachine is integrated with another software (Lightspeed, Quickbooks, etc.), you will only be able to edit customer details and document design.
Products, pricing, ID, and taxes will no longer be editable. In this case, you should void the invoice or create a return. Then you can create another one from scratch as a replacement.
When QuoteMachine is not integrated with any other software, every invoice detail may be altered.
How to access the "edit" mode
From the back-office view of an invoice, the "edit" function will be found behind the "..." button as shown on the screenshot below.