User Exit to check Billing with refence to Ztable

Hi Experts,

We are facing unusual situation where in we need to check the current billing quantity with reference to the quantity stored in ztable (This is order related billing) .

The ztable created with following fields.

1. Quantity (A) .The quantity saved from the Ztransaction .(There is no any other table/transaction in SAP.

2. Quantity build(B): The field should stored from the billed quantity VBRP/VBRK.

3. Available quantity(C = A-B) : The dynamic calculation field . This quantity will be checked against current billing quantity every time before we saved the document.

We are looking for UER EXIT/ INCLUDES where in we can insert the code to carry out to carry the current billing Quantity and check against Quantity available in Ztable. If current billing quantity exceeds the Quantity available it should throw an error before saving the document.

If any of you came across similar situation Please help us by giving Exit Name so that we can code there. Your help on this regard will be highly appreciated.

Thanks and Regards,

Shivakumar K B

+919886920258

Manjunath H S

+919740433511