According to your customer requirement you can choose commitment buget (9I) or payment budget (9H) legers.
A standardized framework for the forecasted expenditures and revenues or the costs, revenues and investments, that can be expected within a fiscal year and area of responsibility.
A standardized framework within a particular area of responsibility for entering commitments that will lead to expenditures or costs in the current year or in subsequent years.
Definition: payment budget
The below link will help to you more understanding.
Just brief info...
The commitments (PR/PO, Funds Reservation, Fund Pre commitment etc.,) will be checked against the commitment budget availability. whereas Invoice is checked against the commitment budget and payment budget.The payment (after RFFMS200) updates uniquely the PB.
Also read the below help link.