Correct - the ex date was September 1. You had already bought the shares with a dividend discount at that time. Therefore, you were no longer eligible for it - only for the next one. You have to buy your shares 1 day before the ex-dividend date to be eligible for the dividend.
I wonder how people think they are ready to invest at all (especially in dividends) when they don't even know the basics and not find out this stuff before they put money in something.