---
title: 1010: Field type. | API Docs
description: A field has the wrong JSON type, or is null where null is not accepted.
---

**HTTP status:** `400` or `422`, depending on the request. May also be reported as a field-level finding in `error.details[]`.

The value at param is the wrong JSON type for the field, or is null on a field the contract does not declare nullable. A top-level body field caught by the decoder answers 400; a field inside a part or a strict body answers 422 with the pointer in details.

## Troubleshooting

- Inspect error.param / details\[].param and the message, which names the expected type.

## Related

- [Part schemas](/channel/whatsapp/api/resources/contract/methods/part_schema/index.md)