No payment shall be made and no obligation incurred by or on behalf of the city except in accordance with an appropriation duly made, and no payment shall be made from or obligation incurred against any appropriation unless the director of finance shall first certify that there is a sufficient unexpended and unencumbered balance in such appropriation to meet the same; provided that nothing herein shall be taken to prevent the advance authorization of expenditures for small purchases as provided for by this chapter. Every expenditure or obligation authorized or incurred in violation of the provisions of this chapter shall be void. Every payment made in violation of the provisions of this chapter shall be deemed illegal, and every official who shall knowingly authorize or make such payment or knowingly take part therein and every person who shall knowingly receive the payment or any part thereof shall be jointly and severally liable to the city for the full amount so paid or received. If any officer, member of any board, or employee of the city, shall knowingly incur any obligation or shall knowingly authorize or make any expenditure in violation of the provisions of this chapter or knowingly take part therein, such action shall be cause for his or her removal. Nothing in this section, however, shall prevent the making of contracts of lease or for services providing for the payment of funds at a time beyond the fiscal year in which such contracts are made, provided the nature of such transactions will reasonably require the making of such contracts.