Error on Line 5 of the schedule 8812

[4father]

I have received a letter from the IRS that I owe an addition $1,000 due to an error in calculating the Child Tax Credit Amount.  I have 3 dependent children aged 21,18, 15 in 2021.  If I am reading the instructions correctly, that means I should get $2,000 (based on the worksheet below.)  The IRS is stating that this should be $1,000.  Are they right?

Worksheet for Line 5 Schedule 8812	Amount
1. Multiply Schedule 8812, line 4b, by $3,600	$                      -
2. Multiply Schedule 8812, line 4c, by $3,000	$               3,000
3. Add line 1 and line 2	$               3,000
4. Multiply Schedule 8812, line 4a, by $2,000	$               2,000
5. Subtract line 4 from line 3	$               1,000
6. Enter the amount shown below for your filing status • Married filing jointly — $12,500 • Qualifying widow(er) — $2,500 • Head of household — $4,375 • All other filing statuses — $6,250	$             12,500
7. Enter the smaller of line 5 or line 6	$               1,000
8. Enter the amount shown below for your filing status • Married filing jointly or Qualifying widow(er) — $150,000 • Head of household — $112,500 • All other filing statuses — $75,000	$          150,000
9. Subtract line 8 from Schedule 8812, line 3 • If zero or less, enter -0- • If more than zero and not a multiple of $1,000, enter the next multiple of $1,000 For example, if the result is $425, enter $1,000; if the result is $1,025, enter $2,000, etc.	$             88,000
10. Multiply line 9 by 5% (0.05)	$               4,400
11. Enter the smaller of line 7 or line 10	$               1,000
12. Subtract line 11 from line 3. Enter on Schedule 8812, line 5	$               2,000

[Critter-3]

Did you get $1000 in advance ?   If so it should be reflected on line 14f  of the form 8812 which will reduce the credit.  

[NCperson]

@4father - check your bank account statements from Jul- Dec, 2021 (around the 15th of the month).   I suspect you'll find IRS deposits over those 6 months and hence Line 14f should have reflected  that.  THAT is why the IRS is making the adjustment.  (14f is filled in by the response to TT question to you, "how much did you receive in advance for the child tax credit" during its interview process).

you received $1000 last year and then $1000 on Line 28 of Form 1040 - is that what occured (or should have occured?)

[4father]

@NCperson @Critter-3  thanks for  the responses.  Spot on.  Received an ACH payment of $166 for 2 months and $167 for 4 months between July and Dec 2021 for an advance tax credit of $1,000.