bad_request

The API returns bad_request with HTTP status 400.

Malformed request body/query, often paired with field errors in details.

#Where the API reference mentions it

• Steps (Campaigns)
• Create a key (API Keys)

#What the response looks like

{
  "error": {
    "code": "bad_request",
    "message": "...",
    "details": null
  }
}

error.code is stable and safe to branch on. error.message is debugging context, not something to parse. The full list of codes, and the rate limits, are on Errors & Rate Limits.