The Finance Director shall not allow the amount set aside for any appropriation to be overdrawn or allow a voucher to be paid unless sufficient funds are actually in the City Treasury to the credit of the fund on which the voucher is drawn. When any claim is presented to the Director, the Director may require evidence that the amount is due, and for this purpose may summon any agent, clerk or employee of the City, or any other person, and examine him or her on oath or affirmation concerning the voucher or claim.