Deductions & credits

Check Schedule 8812 in your tax return to see the details of the Child Tax Credit.   Line 14e will show the amount of the credit you can claim.   But this amount gets reduced by the amount you already received as early payment.   

If you received an advance of $1K, it makes sense that your remaining credit would be $1K also.   The advances were issued for 1/2 the amount you would be expected to receive.   In the example below, $3600 was received early as they were expected to qualify for a $7200 credit.   But, due to higher income amounts, the credit was reduced to $4K, leaving only a $400 credit.