A sales invoice can be edited or deleted only if the customer has not
paid for the item, i.e., the Is Paid checkbox was not selected
when creating the sales invoice.
Click module access icon > Administration > Inventory > Billing to open the Invoice page.
Select a store. All sales invoices of the store are displayed. If you are searching for a particular invoice, select the store and enter the invoice number to search.
Click Edit to edit the sales invoice, or click Delete to delete the sales invoice.
For more information, watch this-