Return Json From lambda Go in ApiGateway

Im trying to make this work, what i want is to get json as output from lambda when called from API gateway with some nested json.

This is what i expect,

{
"data": {"username":"Random User","Age":20}",
"message": "This is sample"
}

but im getting escaped json
{
"data": "\n\t{\n\t\t\"username\":\"Random User\",\n\t\t\"Age\":20\n\t}",
"message": "This is sample"
}

the sample code which im trying

package main

import (
	"encoding/json"
	"log"
	"net/http"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"
)

type Response struct {
	StatusCode int               `json:"statusCode"`
	Headers    map[string]string `json:"headers"`
	Body       string            `json:"body"`
}

type RequestBody struct {
	Data    any    `json:"data"`
	Message string `json:"message"`
}

const (
	data string = `
	{
		"username":"Random User",
		"Age":20
	}`
)

func EventHandler(request events.APIGatewayProxyRequest) (Response, error) {
	response := Response{}
	log.Println(request.Headers)
	body := RequestBody{Data: data, Message: "This is sample"}
	b, _ := json.Marshal(body)
	response.Body = string(b)
	response.StatusCode = http.StatusOK
	log.Println("Before Return")
	return response, nil
}

func main() {
	lambda.Start(EventHandler)
}

The application encodes the JSON in data to JSON. Use json.RawMessage to eliminate the extra level of JSON encoding.

var data = json.RawMessage(`
    {
        "username":"Random User",
        "Age":20
    }`)

This is because to marshaled (encoded as JSON) a string that already contains a JSON object. Instead, try this:

var data = map[string]any {
        "username":"Random User",
        "Age":20
    }

Or you can also do:

    body := RequestBody{Data: json.RawMessage(data), Message: "This is sample"}