> I would guess that my biggest issue is not the details of the IAP, but rather marketing. I don't really do much of it outside the occasional tweet or social media comment. These blog posts are my primary marketing strategy.

Spot on. Makers think releasing the product is the end. It’s actually just the beginning. Now that your product is released, you will live and die by the sword of marketing.

As an indie developer, I made a month worth of sales in 3 days when a YouTuber mentioned my app. Not even a big YouTuber (few tens of thousands subscribers).