If you have children and received child tax credit payments in 2021, you'll need a "Letter 6419" from the IRS to complete your tax filing, reconciling the amounts received with what you were eligible for. The IRS has mailed out Letter 6419 but now says "some" of them are wrong.
The IRS says they've identified two errors. One is if someone's December advance payment was returned by the bank or the Postal Service. The other is divorced taxpayers who alternate tax benefits associated with their children every other year. However, as tax analyst Amber Gray-Fenner observed: "Tax professionals on social media are increasingly reporting errors on Letter 6419 that cannot be attributed to returned payments or custody arrangements. Indeed, some of the incorrect letters are being received by tax professionals themselves." In some cases, the Letter 6419 amounts do not match bank deposits and IRS account transcripts. Astonishing that the IRS is putting stuff out that doesn't match those amounts.
Every taxpayer should cross-reference their Letter 6419 with what was actually deposited. The IRS has not acknowledged this problem yet and so has not given any guidance on what taxpayers should do. One option if your 6419 doesn't match deposits is you can request an account transcript and that supersedes an incorrect Letter 6419. (And let us know if your 6419 is correct or incorrect, we're trying to find out how big this problem is too.)