This is a new procedure the IRS started last year for TY2024. It allows returns that claim dependents who have already been claimed on another taxpayer’s return to be efiled.

If a dependent has already been claimed on a previously filed return and your client's return is rejected, the client can get an Identity Protection Personal Identification Number (IP PIN) for the dependent and you can re-...

Like Terry53029 said, this only allows you to efile the return. It doesn't resolve the fact that the IRS has two tax returns claiming the exact same person, so they will still investigate.

Here are some good references:

IR-2024-294

Age, name or SSN rejects, errors, correction procedures

Protect Yourself From Tax-Related Identity Theft: Get an Identity Protection PIN