CP23 IRS corrected your return because it found a difference between the amount of estimated tax payments on your tax return and the amount it posted to your account. you'll need to respond to the notice by providing proof of each and every estimated tax payment you made. you can use bank or credit card statements. It would also help if you circled or highlighted the payment on the statement.
you can go to the IRS website and look up online what the IRS shows. if you can identify which payments or payments are missing you may need to only send proof for those. It would be the account transcript. if you don' want to register you can request it by mail
https://www.irs.gov/individuals/get-transcript
