I received a cp523k notice to maintain the payment plan. When I go online to make the direct pay it asks for me to choose a payment type. What payment type do I choose?

This payment is due immediately to avoid defaulting on the existing payment plan. So I want to make sure I do the direct pay accurately and it isn't clear which payment type to use. I received 3 certified letters for the same amount due but list a different year covered in the payment plan.