if your daughter is a covered dependent her Modified Adjusted Gross Income would go on line 2b. adding a dependent will increase the federal poverty line but it may also increase family income so it is unknown how household income as a % of the poverty line will be affected. do an amended return but be sure to include her MAGI on line 2b (usually her regular AGI + tax-exempt interest - assuming she filed a 2019 tax return). then see what the revised 8962 shows. if it shows less than what the IRS is asking, send in the amended return signed and dated with a copy of the notice a letter of explanation (you added your daughter to your return and her MAGI of $xxxx to form 8962 line 2b resulting in ........ to the address on the notice and any payment due. the IRS will bill for penalties and interest.
if you are still over 400% send the IRS the money or make payment arrangements.
