Correcting for over-reported Sales from previous year

[Anton777]

My former accountant overreported Gross Sales (as well as net earnings) of my S Corporation in 2019 by including a $3000 invoice paid to me after year end - essentially applying accrual accounting while using cash method. I don't want to amend the 2019 return. If I now exclude this item from 2020 Sales, do I need to report this discrepancy somewhere, e.g. on Schedule M-1 or M-2?

[Mike9241]

technically you're supposed to amend or justifiably go back to the accountant and tell him/her to amend the returns for free.  if refused and the accountant is a CPA you can report them to your state's CPA society for unprofessional conduct. here's the tax trap of not amending. a few years down the road when you can no longer amend 2019 the IRS comes in and audits finding that "adjustment".  they have every right to add back that adjustment to the 2020 return, so you would end up paying taxes on it twice. 

can't tell you what to do in relation to the return because that would depend on how the extra $3K was included in income - either an asset like cash needed to be overstated or there was an m-1 adjustment.  

[Anton777]

Thanks, @Mike9241. It was included in Accounts Receivable.

She already amended that return once (this wasn't the only error), plus I would have to amend my personal as well, so I hope to find another solution even if it's not perfect. 

I see that schedule M-2 part b on 1120S specifically lists "Shareholders Undistributed Income Previously Taxed", which seems to be a good fit. Or is this referring to something else?