It just means there was an attempt to access return or refund results using the wrong Social Security number or TIN. Make sure you access "where's my refund" with the SSN that was listed first on the return.
What IRS Code 9001 Really Means
The actual code tells you exactly what it means – you filed a tax return that had multiple Social Security numbers attached to it. Typically, this is a husband and wife, but it could also include children as well (you never know, adult dependents may be checking the status of the refund). When you file your tax return, you have to specify a primary taxpayer, and the spouse or children all are secondary.
If you login to Where’s My Refund or on the IRS App and try to use the secondary Social Security number, you’re going to get this error message.
Having code 9001 is not an audit, and it shouldn’t concern taxpayers. It just means there was an attempt to access return or refund results using the wrong Social Security number or TIN.