From my observations, there are communities which has strict moderation policies, but sometimes they do allow posts if the incentives are right. That's why I mention writing an essay instead of posting a link. I feel like if it's a well known pain-point and the community is aware about it, and you outline why your motivation for solving it, it will resonate. Instead of promotion, you're posting your story.

Again, this strategy could fail too, but I've always noticed if you take one topic, there are multiple subreddits that address it, so you'll have luck in at least one of them. What market is your product targeting?