Using an API key in Amazon API Gateway
The x-api-key parameter is passed as a HTTP header parameter (i.e. it is not added to the JSON body). How you pass HTTP headers depend on the HTTP client you use.
For example, if you use curl and assuming that you POST the JSON payload, a request would look something like (where you replace [api-id] with the actual id and [region] with the AWS region of your API):
$ curl -X POST -H "x-api-key: theKey" -H "Content-Type: application/json" -d '{"key":"val"}' https://[api-id].execute-api.[region].amazonaws.com
I had to add an API Usage plan, and then link the plan to the API stage.
Seems like this is the only way to link the key to the API, not sure if this is a recent change on AWS.
If you set 'API Key Required' option to true, please check below.
you have to pass 'x-api-key' HTTP Header Parameter to API Gateway.
The API Key had to be created.
In addition, you need to check a Usage Plan for the API Key on API Gateway Console.