I have a small business in Ontario Canada and I file my taxes each year. Let's say I discover an erroneous invoice from the last fiscal year for which I've already submitted my tax returns to the government. Hence, it was part of the reported taxable income. The invoice was an erroneous duplicate that was never paid and it was never sent to my customer.
What is the proper accounting approach to remedy this situation after the fact? If I try to edit the original invoice within the fiscal year that it was issued, that means I have to get an accountant to send an amended return? Or am I to just create a new invoice in my current fiscal year with the same but negative amount as the original invoice ? Or should I be issuing a credit memo against my original invoice?
I tried to search for this problem on the internet, but I couldn't find a comprehensible answer that deals with erroneous invoices in previous fiscal periods.
I am using accrual based accounting method.