If needed, an inspector can void (retract/cancel) an invoice if the status of the invoice is Approved, Disputed, or Pending.
1. On the invoice, select the Actions drop-down menu and select Void:

2. Submit a comment as to why the invoice is being voided and then select "Void":

NOTE: Voiding an invoice cannot be undone and a new, unique invoice number must be assigned.
If the invoice is a main invoice, no further supplemental invoices can be created. The invoicing process should begin anew
See: Creating Supplemental Invoices