Errors

Errors use Problem Details (RFC 9457), with Content-Type: application/problem+json:

{
  "type": "https://stable-pro.com/docs/api/problems/forbidden",
  "title": "The API key lacks a required permission",
  "status": 403,
  "detail": "La chiave non ha il permesso receipts:read: lo può accendere il titolare della scuderia in Impostazioni → Collegamenti.",
  "missing_permission": "receipts:read"
}

• Decide on type: it is stable and in English, and it is the address of the page that explains it. The title is in English too.
• detail is a sentence for people, in the requested language (?lang=, Accept-Language): show it, never parse it.
• Some types carry extra fields: reason (401), missing_permission (403), invalid_param (400).
• Error bodies are open: a new field can arrive.