Ask IH: What's the biggest technical mistake you've made with your product?

I've been having trouble onboarding new customers to my SaaS (https://eatcake.app).

My app was "working" correctly, all my tests were passing, but for whatever reason, when users would try to create a new subscription, it wasn't getting passed back to my system. This was confusing customers because they assumed something was going wrong and so they would try again, and again, and again. All the while they were getting charged $10 for the privilege!

I guess this was just one of those lightbulb moments, but going through a test purchase locally, seeing it all work as expected, then going to production and trying it again and comparing the results, it became painfully obvious. I had never thought to try it all back-to-back on both systems so close together.

Stripe was only configured to send webhooks for 5 events, none of them relevant to my app. 🤦‍♂️ I think this was because of a previous venture I had setup in the same Stripe account that I repurposed for this new venture.

I've been manually copying customers subscription details into my app for 6 months.

TL;DR: Check your Stripe webhooks.

What's the biggest technical screw-up you've add in your project so far?