How to complete the challenge PUT /api/todos/{id} no amend id (422)

By Alan Richardson · Published 2026-07-20

Issue a PUT request to an existing todo and include an id in the body that does not match the id in the URL.

The response should be 422 Unprocessable Content because the API does not allow the primary key to be amended through the request body.

Look for the validation message containing:

Can not amend id from

Try it now

If you don't know what todos are available then you can check by GET /api/todos. See the solution.

GET /api/todos to see what todos are available now

If you have already deleted all todos, create one using POST /api/todos. See the solution.

POST /api/todos to create a todo item for this challenge

PUT /api/todos/{id} with a mismatched body id to trigger 422

Lessons Learned

• A body id that conflicts with the URL id is rejected to protect resource identity.
• PUT updates should not allow clients to rename or move a resource accidentally.
• Identity mismatch tests are most useful when all other fields are valid.

Suggested Experiments

• Send a matching body id, then change only the body id and compare 200 OK with 422 Unprocessable Content.
• Change only the URL id while keeping the body id fixed to see the same mismatch from the other side.

Experiment with this endpoint