Came across a service last week with a free trial and paid plan. How to upgrade? Contact by email! Why spend time and resources on a payment process if you don'

Came across a service last week with a free trial and paid plan. How to upgrade? Contact by email! Why spend time and resources on a payment process if you don't have any paying customers yet? Obviously not right for everyone, and I'm not saying it doesn't have its own challenges, but the core product deserves the most attention early on.