A notice calling for bids for each proposed issue of municipal bonds must be published at least once in the official newspaper of the municipality, or, if the municipality does not have an official newspaper, then in the county’s official newspaper, not less than ten days nor more than thirty days before the date specified therein for the receiving of such bids. Such notice may be in any form but must specify the amount of bonds offered for sale and the date of the maturity thereof. Failure to publish such notice does not impair the validity of such bonds but renders unenforceable any executory contract entered into for the sale thereof.