Precoro makes the calculation of your budgets and allows to create Purchase orders and Bills only for the available budget sum.

This is made to restrict exaggerated budget usage and track resources available for future purchases. 

The available budget sum is counted by the following form 

Available sum=Budget sum - the sum of the Purchase orders that do not have bills created - Sum of the bills created manually (without Purchase orders) - the sum of the Bills created on PO - the sum of Purchase orders available for further Bill creation.

For example: 

The budget amount is 5000 USD. They have Bills for 500 USD created from Purchase orders, bills created manually sum is 250 USD and we have bill created from PO's for 1750 USD. Also, we have 1 Purchase order o for total sum 1000USD and only one bill created for it for 550 USD, although the PO sum for this bill was 500 USD. 

My budget sum will be:

5000 - 500-250-1750-550-500= 1450 USD