Notice CP504B is not the first notice that you received. There must have been an earlier notice that told you what was wrong in your tax return, and several more notices that you did not respond to. Now it has gotten to the point where the IRS is going to seize your assets to cover the tax that you owe. You need to go immediately to a tax professional who is experienced in handling IRS problems. You cannot do it yourself, and you cannot do it with advice from the internet. See Understanding your CP504B notice on the IRS website for more information.
