Launch error 400

Hello,
I've been doing some flask and graphql practices. I made mutations, the proof of concept went well until I had to validate the data entry by the user.

Usually in api rest, I release a
`make_response(jsonify(error="my error"), 404) `
but with graphql I haven't found a way to launch a 400. All codes are 200.

Someone can explain to me a little more and how I could launch an error 400 when the user's input is not valid.

Thanks