If you are Cost Eng'r, the PM tells you to process a billing to be paid in petty cash instead of the invoicing (billing procedure), what will you do?

I will reject his request, because petty cash balance kept in project to meet the urgent disbursement requirement, also there is a limit for billing from site (at our site as per company policy5000 SR), so he cant process a bill more than allowed.

That depends on liquidity available on company as usually paying conditions for suppliers after month or two of receiving supplies on the other hand petty cash mean to instant invoice client and also depends on importance of supplies to be wait or immediate invoicing