Why isn’t my tax credit calculated and my marketplace not calculated correct

What "tax credit $1200"  do you mean?

No one can see your screen or your tax return.   The child tax credit  can reduce the amount of tax you owe.  Were you expecting to get it all back as a refund?   Your refund is determined after the credits are used to pay any tax you owe, so that may explain the refund you are seeing.

And...at best, the refundable amount of the child tax credit is $1700---not $2200.   The refundable amount is based on how much you earned from working.

  The maximum amount of the child tax credit is now $2200 per child; the refundable “additional child tax credit” amount is $1700.   In order to get that credit, you have to have income from working.  

Take the amount you earned from working.   Subtract $2500.   Multiply the rest by 15%.  That is the additional child tax credit per child that you can get—- up to the maximum of $1700 per child.   If the amount you earned from working was low, you will not get the full $1700 per child.

And for the Earned Income Credit—-

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-credits-deductions/qualifications-earned-income-credit-eic-eitc/L7w4BFP32_US_en_US?uid=m62rmz09

https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/use-the-eitc-assistant

https://www.irs.gov/pub/irs-pdf/p596.pdf

Look at your 2025 Form 1040 to see the child-related credits you received

PREVIEW 1040

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/preview-turbotax-online-return-filing/L77WCkvnu_US_en_US?uid=m681fkhr

Child Tax Credit line 19

Credit for Other Dependents line 19

Earned Income Credit line 27

Additional Child Tax Credit line 28

It depends. Not all credits turn into cash. There's a refundable portion of the Child Tax Credit per child, and the rest is non-refundable. It's also dependent on your income and other household factors.

If by Marketplace, you are referring to  the Premium Tax Credit, this isn't automatically a refund. This amount is entered on Form 8962 and depending on your income, and other household factors, it can be reduced dramatically. 

Without additional information, it's unclear what could have caused your refund amount to be reduced. More than likely, it could have been:

1. Your tax liability absorbed most of the non-refundable Child Tax Credit
2. Your additional Child Tax Credit was capped
3. Your premium tax credit was reduced or offset