Stop manager to distribute over budget

Summary:

Restrict Manager not to enter over budget

Content (required):

We have 100000 budget which distributed to direct manager, now each manager have 20000, Now when each manager further break it to their sub manager but they can enter more than 20000 which system shows as negative values, How can we stop manager don't distribute over budget like 21000.

Version (include the version you are using, if applicable):

21D

Code Snippet (add any code snippets that support your topic, if applicable):