You need to under promise and over deliver with your new startup. Everyone loves a good comeback story, use this to your advantage. After you've started to over deliver for your clients, ask if they would write about their experience in exchange for xyz.

After a few have done that, write a post titled "How my failed startup helped me succeed" or similar. In this post be very transparent about why your first startup failed to deliver, but don't ever put blame on anyone but yourself. Take responsibility for the failure. Talk about what you learned and how those lessons are helping you deliver for your current clients. In your post link to the articles your current clients wrote and briefly mention why they're happy.

Afterwards, promote the shit out of your post.

What this accomplishes:

1. It takes away any power a person would have in bringing up your past failure because you've spun it in a positive way. This will give you the confidence to talk about ideas moving forward. You will always be able to take negative criticism of your past failure and spin it to talk about how it lead to your current success.

2. You've given people a good story. People like good stories, and they love good story tellers.

3. Using your current clients endorsement you prove that you can deliver.

Just some rough thoughts. Sorry for the bad grammer. I just don't care enough to correct them. Hope this helps.