Designing a Transaction ID for a Payment System: What I Learned

Recently, I worked through the design of a 10-character customer-facing transaction ID. It looks trivial. It is not. Here's the journey, and the design that survived. THE CONSTRAINTS Exactly 10 characters Alphanumeric Globally unique, forever Customer-facing — read aloud, typed on phones, screenshotted, dictated to support agents That last point is what makes this hard. An internal ID can be ugly. A customer-facing ID has to survive the real world. THE OPTIONS I CONSIDERED Sequential counter (1,