Building a Payment Processor: My First Attempt Was a Disaster

I wanted to figure out how people build payment systems without losing everyone's money. It turns out, my first attempt was a great way to lose a lot of it. I started with what felt like a simple Go service. One endpoint, one database table, and a third-party provider to handle the actual charging. The plan was straightforward: Decode the request. Call the provider to charge the user. Save the result to my database. Respond with a 201. It looked like this: func ( s Server ) createCharge ( w http