A failed API response should help explain the problem. Review it from the customer's and support team's perspectives. START WITH SCENARIOS In a test environment, prepare a missing record, an invalid parameter and a temporary failure. For each, write the user's expected next step, such as correcting input or trying later. Do not create real orders merely to test messages. A SHARED STRUCTURE RFC 9457 defines Problem Details for HTTP APIs and the application/problem+json media type. It distinguishes the problem type identifier, type, from detail explaining an individual occurrence. Clients need not guess a new error structure each time. SEPARATE THE AUDIENCES Customers need a short next step; developers need a stable way to identify the situation. Do not base application logic solely on translated message text. Agree which information may be public, and keep passwords, tokens, internal queries and private conversations out of responses. CHECK THE WHOLE PATH Save a safe response example and inspect how the interface presents it. Does a form mistakenly turn every failure into success? Can support locate the inquiry without asking for secrets? Assign an owner and completion criterion to each scenario. When planning a website for a domain from the catalogue, include failure examples alongside successful journeys in the brief. This makes behavior discussable before launch, rather than after the first confusing support request. Image: a new AI photoillustration for this article; a conceptual scene, not a documentary photograph. Domain catalogue: https://domainevery.com/en/domains Primary sources: https://www.rfc-editor.org/rfc/rfc9457.html
