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@Opfor77 wrote:

 How do I remedy this so new client has income and expenses through a SCH C,

and ex doesn't have to claim income that's not hers?

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Report the income and expenses on Schedule C.  There is no need for a 1099-K, 1099-NEC, or 1099-MISC to report income.

The ex can just not report the income, and if she gets an IRS notice, respond to it explaining the situation.  Or possibly report the income, then send your client a 1099 as a "nominee" to back out that income.