This article details the easiest and safest ways to pay your IRS CP303 balance. Whether you're paying online, by mail, or arranging a payment plan, this step-by-step guide helps you settle your tax liability with confidence. This article details the easiest and safest ways to pay your IRS CP303 balance. Whether you're paying online, by mail, or arranging a payment plan, this step-by-step guide helps you settle your tax liability with confidence.