If you have successfully negotiated an installment agreement with the IRS, congratulations! You no longer have to be constantly looking over your shoulder for threatening letters, property liens, or visits from revenue officers.
Depending on your circumstances and the amount due, the hard part could be over, or it could be just beginning as you start making payments. The important thing to remember is that the major condition of your installment agreement is that you make all of your payments in the agreed-upon amount on time.
Once you have made several payments, it is not the time to start slacking off on your responsibility. The IRS might excuse a late or missed payment or two if you have a really good excuse and it does not become a habit. After all … life happens. An emergency or some other unforeseen issue may cause you either be late with your payment or unable to pay it at all.
If it appears to the IRS that you are not taking your installment seriously; if they discover after the fact that you submitted erroneous information on your application or you just stopped paying at all, you will be considered in default. And that is not a good position to be in. If you are in default on your installment agreement, the IRS has the option to terminate it and you will be back at square one with a big tax debt and no way to pay it.