I purchased a new home.My buyer's agent paid me cashback and asked W-9 from me but didnt issue any 1099 form.Is this cashback taxable?How to handle this while filing tax?

Cashback amount is around $20K. He asked w9 from me but didnt give any 1099MISC or 1099NEC or any form to me. Do i need to declare this while filing tax? Is this taxable income? What's the best way to handle this?