Any capital facilities fees paid prior to March 24, 1988, and not protested or challenged pursuant to law on or before January 1, 1987, shall not be subject to refund, except for capital facilities fees paid after July 21, 1986, by a public agency subject to Section 54999.3 that are in excess of the maximum amount authorized by Sections 54999.3 and 54999.35. Agreements entered into prior to or after March 24, 1988, for the payment of capital facilities fees or capacity charges shall be effective.