The hardest part of learning API testing isn't Postman. Postman is fine. The hard part is finding something to point it at.
I learned this the annoying way. When I started, our staging environment was the only API I had access to, and it was down roughly one day in three. When it was up, half my requests failed for reasons that had nothing to do with what I was practising — expired tokens, a colleague mid-deploy, a database someone had just truncated. I spent more time asking "is it me or is it the environment?" than actually learning.
So I went looking for a sandbox. Public APIs are easy to find, but most of them are read-only. You can GET all day and never touch a POST, never see a 401, never write a test that fails on purpose. Which is a problem, because in real QA work the interesting bugs live in the write paths and the error responses.
Then I found funapi.dev. It's a set of mock REST APIs — 37 of them, everything from a pizza ordering service to an OAuth 2.0 playground — built specifically so you can practise against them. No signup, no API key application form, no rate limit emails. And crucially, they're designed to return every status code you'd want to test, including the ugly ones.
