validation-failed

HTTP 400. The request reached the endpoint but one or more parameters did not match its schema.

Unlike the other problem types, this one carries an extra errors array naming each field that failed — permitted by RFC 9457 §3.2, which allows additional members on a problem document.

Code
{
  "type": "https://developers.supliful.com/errors/validation-failed",
  "title": "Request validation failed",
  "status": 400,
  "detail": "One or more request parameters are invalid.",
  "instance": "/v1/example",
  "errors": [
    { "path": "quantity", "message": "Expected number, received string" },
    { "path": "address.zip", "message": "Required" }
  ]
}

Reading the errors array

Each entry has:

• path — the location of the offending value, dot-joined. Nested objects read as address.zip; array members include their index, as lines.0.sku.
• message — what was wrong with that specific value.

The array names every field that failed, not just the first, so a single round trip tells you everything you need to correct. There is no need to fix one field and resubmit to discover the next.

How to fix it

Read the path values against the endpoint's schema in the API Reference, which is generated from the same definitions that perform this validation — so the reference and the validator cannot disagree.

The usual causes:

• A number sent as a string, typically from a template or a form encoding ("3" where 3 is expected).
• A missing required field, reported as Required.
• A timestamp not in ISO 8601 form.
• A field name that is close but not exact — casing and pluralisation are significant.

Retry behaviour

Terminal. The same request will fail identically until the payload changes, so do not retry it unmodified. Log the errors array — it is the whole diagnosis, and it is not recoverable from the status code alone.