In contract, award to john supply & install gate. but kelvin installed it & got his money. Deduction to john should in-to 'omission' or 'debit note'?

I AGREE WITH BOTH ANSWERS PREVIOUS 

Since the payment to Mr. John is vouched on the basis of the Agreement (Contract), John's account is mandatory to reflect the history.  The Deduction to John based on "Debit Note" is appropriate and the correct practice to be followed.

Award to john in contract with supply & install, but he just only supply without install. site supervisor find kelvin to install it. So kelvin had got his installation fees. In payment,