I'd suggest trying to get some kind of endorsement / verification from a government entity or something like a law firm, or any other entity that will boost you

I'd suggest trying to get some kind of endorsement / verification from a government entity or something like a law firm, or any other entity that will boost your credibility. Then display such endorsement on the first screen the user sees when accessing your app. I think people are scared that your app is not legitimate and the information they share could be used to harm them.