Money Don’t throw away this document. Why IRS Letter 6419 is critical to filing your 2021 taxes. January 23, 2022January 25, 2022 Susan Tompor, Detroit Free Press Comments Off on Don’t throw away this document. Why IRS Letter 6419 is critical to filing your 2021 taxes. Many parents could toss a key tax-related letter from the IRS relating to child tax credit payments in 2021. Here's what IRS Letter 6419 looks like.