If you’re making a payment under an agreement (like an installment plan), send it to the specific address listed in your agreement. Not the general one. The IRS is way more likely to lose your money if you ignore the special instructions. And if you’re paying an Offer in Compromise? Use the designated P.O. box in Memphis. I’m not kidding—the IRS has a different processing center for every mood.
Also, always include a payment stub or a note with “Installment Agreement” written in red. That way, they don’t apply your payment to a random old penalty from 2016 when you were living on a houseboat in Florida. You’d be amazed how often that happens.
