Project Costing (Top-Down budget integration): Budgetary Control by Project Level setup steps ---Pl

Dear all,
Please guide me, "Can and How" to setup "PROJECT" Level Budget Control.

For example, a Project has 2 tasks with an expenditure type in each task. Project Fund available of each task, is 30 and 40 respectively, then total fund available of project is 70. If user submits a pr (or po, invoice, ..) amount 50, the system allow this transaction to passed fund checking because of fund available in project level.

I have already set Project > Budget Control > Level > Project = Absolute, and leave Task and Resource = None

Please help and describe in detail.

Thanks in advance.

Best regards,
Learner