The body response of Lambda must output a format that is acceptable to AWS API Gateway. An example NodeJS code with the appropriate callback will ensure a successful 200 OK response:
'use strict';
console.log('Loading function');
exports.handler = (event, context, callback) => {
var responseBody = {
"key3": event.queryStringParameters.key3,
"key2": event.queryStringParameters.key2,
"key1": event.queryStringParameters.key1
};
var response = {
"statusCode": 200,
"headers": {},
"body": JSON.stringify(responseBody),
"isBase64Encoded": false
};
// In order for AWS API Gateway to work, the response must
// be in the format of the "response" variable as shown above.
callback(null, response);
};
You can find more information from the sources below.