If possible, he should try to reach out to Google Adsense to see if they can confirm all payments will be reported as being under the LLC's identification number instead of his SSN. Assuming this is for 2024, no tax forms have been mailed out yet and therefore, the company may be able to correct the error so all payments are reported under the LLC when Form 1099-NEC is issued.
If this is related to 2023, he can request that the company issue a corrected 1099-NEC form to show no amounts being reported to him and then issue a new 1099-NEC for those payments under the LLC's identification number. If he has already filed the partnership and personal returns, he may need to file amended returns to reflect any corrections made on Form 1099-NEC.
As a last resort for 2023, another option is to report the 1099-NEC on his personal return as it is reported under his SSN, and then show a corresponding reversal of the income on his 1040 with a description that the income is being reported by the LLC and include the LLC identification number so the IRS can cross reference the amount to ensure it is being reported on the LLC return.
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