At the moment, purchase agreements are the way to handle blanket POs which unfortunately is not tied to budget control. Multiple POs will need to be raised to draw down on the amount.

Hoping PRs/POs (service-related) can be raised directly based on amount. The quantity aspect is set to 1 and will not cause validation errors as long as it is within the set amount. Whenever an invoice comes in, it should just draw from the amount of the PO. This way, only one PO number will be given to the vendor as reference for the entire duration of the service/agreement. For reference, please check how the service PO/service entry sheet module works in SAP.