The Medicare Prescription Payment Plan is a  payment option in the prescription drug law that works with your current drug coverage to help you manage your out-of-pocket costs for drugs covered by your plan by spreading them across the calendar year (January–December). Anyone with a Medicare drug plan or Medicare health plan with drug coverage (like a Medicare Advantage Plan with drug coverage) can use this payment option. All plans offer this payment option, and participation is voluntary.

If you select this payment option, each month you’ll continue to pay your plan premium (if you have one), and you’ll get a bill from your health or drug plan to pay for your prescription drugs (instead of paying the pharmacy). There’s no cost to participate in the Medicare Prescription Payment Plan.

Source: https://www.medicare.gov/prescription-payment-plan