follow the instructions in the notice to contest the IRS findings. this would include sending a copy of the front and back of the canceled check. enclose a letter that is signed and dated saying that you are enclosing a copy of the extension payment you made in the amount of $1900 that has not been included in the payments shown in the notice and assuming the extension payment was timely state that in your response
in the future you may want to use the IRS website to make an electronic payment on the date you specify. you can get an automatic federal extension without filing form 4868 by making an electronic extension payment.
