If you receive a CP 523 Notice from the IRS (check the computer code on the letter), it means the clock is ticking. Seriously ticking. The CP 523 Notice tells you that the IRS is about to terminate an installment agreement that you set up with the IRS to pay your tax, and then the IRS will seize your assets. This is what the IRS sends out when you default on your payment agreement.
What Do You Do Now?
The best thing you can do now is, before the termination date in your notice, make your payment to the IRS. You can do this on the IRS website. You also need to contact the IRS right away to see if you can reinstate your agreement, and you might have to pay a fee.
Read your notice carefully as it will explain your options. Act right away, including calling a tax professional to discuss all of your options. You have 30 days to contact the IRS, but you should contact your tax professional immediately to discuss options such as The Fresh Start Initiative and the Offer In Compromise Program, which might be available to you.