Hands down, the best (free, no email) resource to learn Effect is here https://www.typeonce.dev/course/effect-beginners-complete-ge..., as opposed to the docs. The link referenced gives a holistic view of how to incorporate it.
await fetch(…)
.catch(e =>
new CustomError(…))
FP always goes out of the way to avoid using the language it operates in and to criticize the ways of doing something it just imagined. As if it wanted to stay as noble from unwashed peasants as it could, but has to do the same job to keep existing.
how to test () => makePayment()? (from the link)
You don’t. You test constituents like request body generation and response handling. It’s inside. You can’t test your Effect-version of this code neither. It’s a strawman.