If someone (or several people) isn’t listening to your ideas or taking you seriously, instead of getting upset, reflect about why are they are not taking you seriously.
It could be something about them. They might not have faith in themselves and they are projecting that back at you.
It might be something about you – how you are showing up in their life. It is worthwhile to reflect: “What is going on with me behind the scenes that they are not believing me?”
It might be that somehow you have lost credibility with them. People look at your track record to get a sense of how credible you are. Maybe you don’t keep your word to yourself, or you don’t have a track record of making such things actually happen, or you haven’t put much effort into making this new venture actually succeed (or at least they haven’t seen it).
You can turn that around quickly. Outline the steps you will take to get the results you are aspiring to. Make your effort and work more visible. Stick to your plans. This will put the validity of your idea into perspective and show people you’re serious.