(1) Before any obligation against the county shall be paid or any disbursement warrant or voucher issued therefor, a detailed invoice or statement approved by the head of the office, department or agency for which the obligation was made shall be filed with the director of accounts and budgets.
(2) The director shall make a careful preaudit of such invoice or statement, including a comparison with any encumbrance document previously posted or filed authorizing such obligation, and shall approve for payment only such items as appear to be correct, properly authorized, and not exceeding the otherwise unencumbered balance of the allotments or appropriations against which they are chargeable.
(3) Disbursement warrants shall be promptly prepared for all such approved items by the director and mailed or delivered to the payees thereof.
(4) A duplicate copy of all disbursement warrants, with all original invoices or other supporting documents, or both, attached to the duplicate copies, shall be kept on file in the office of the director.