The IRS give guidance on this specific topic. Pay specific attention to the S/C Corporation rules. Paying Yourself
It sounds more like a buy out or sale of his share of the S corporation on his end and a purchase of his share by the S corporation. If this is the case it would be an equity transaction and not commissions. However, you indicated this was paid after he had relinquished his ownership. If the latter is true and you don't have documentation before he relinquished his share of the company, indicating he would be paid a commission, then the question still remains about whether he is an employee or an independent contractor.
I would suggest you have a professional prepare the return for 2021 to avoid any future penalties as indicated by @Mike9241.
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