Why does it say I only qualify for $2000 child tax credit? I thought it went up to $3600 this year.

[xmasbaby0]

Q C4. How does the first phaseout reduce the 2021 Child Tax Credit to $2,000 per child? (added June ...

A4. The Child Tax Credit begins to be reduced to $2,000 per child if your modified AGI in 2021 exceeds:

• $150,000 if married and filing a joint return or if filing as a qualifying widow or widower;
• $112,500 if filing as head of household; or
• $75,000 if you are a single filer or are married and filing a separate return.

The first phaseout reduces the Child Tax Credit by $50 for each $1,000 (or fraction thereof) by which your modified AGI exceeds the income threshold described above that is applicable to you.

Q C5. How does the second phaseout reduce the remaining $2,000 Child Tax Credit? (added June 14, 202...

A5. The Child Tax Credit won’t begin to be reduced below $2,000 per child until your modified AGI in 2021 exceeds:

• $400,000 if married and filing a joint return; or
• $200,000 for all other filing statuses.

The second phaseout reduces the Child Tax Credit by $50 for each $1,000 (or fraction thereof) by which your modified AGI exceeds the income threshold described above that is applicable to you.

[KrisD15]

It does subtract your advance payments, did you account for that? 

The credit is also reduced for income limits. 

"The first phaseout can reduce the Child Tax Credit to $2,000 per child.

That is, the first phaseout step can reduce only the $1,600 increase for qualifying children ages 5 and under, and the $1,000 increase for qualifying children ages 6 through 17, at the end of 2021.
The second phaseout can reduce the remaining Child Tax Credit below $2,000 per child.

 The Child Tax Credit begins to be reduced to $2,000 per child if your modified AGI in 2021 exceeds:

$150,000 if married and filing a joint return or if filing as a qualifying widow or widower;
$112,500 if filing as head of household; or
$75,000 if you are a single filer or are married and filing a separate return.
The first phaseout reduces the Child Tax Credit by $50 for each $1,000 (or fraction thereof) by which your modified AGI exceeds the income threshold described above that is applicable to you.

@kevinyk