How to get AWS API Gateway to validate JSON Body against Model

The newly released "x-amazon-apigateway-request-validator" (in April I believe) is supposed to be able to run a JSON schema validation against the POST/PUT payload of an API. I've tried to implement this in several different ways now but I can't make it work. I have added the validators:

"x-amazon-apigateway-request-validators": < "ValidateBody": < "validateRequestParameters": false, "validateRequestBody": true >, "ValidateHeaders":

> For any methind I will look for specific headers so I also have the parameters in the "root" of the Swagger:

"x-amazon-apigateway-request-validator": "ValidateHeaders" 

In the POST I have a x-amazon-apigateway-request-validator: ValidateBody and then a Model with the JSON schema where several elements are required . I can however POST anything as long as it is JSON. There is no validation against the JSON schema done. What am I missing?