Unable to use Lambda proxy integration in API Gateway

[MCoLoL]

Hello,
i'm trying to do an integration with API Gateway and Lambda with the "Proxy integration".
I configured the bash script with the response as described in the documentation.

echo "{\"success\": true}" >&2
or this for apigw
"{\"isBase64Encoded\": false,\"statusCode\": 200,\"headers\": { \"Access-Control-Allow-Origin\": \"*\"},\"body\": \"OK\"}"

but seems that the script is not exiting succesfully and then apigw will response with a 500.
In the log of API GW seems that there is a RuntimeErrorException and the script exit with 6.

Those are the logs:

(a4be7bdd-e53a-409a-b804-28f9129cde0b) Endpoint response body before transformations:
{
"errorMessage": "Exited with code 6",
"errorType": "RuntimeErrorException",
"stackTrace": ""
}
(a4be7bdd-e53a-409a-b804-28f9129cde0b) Lambda execution failed with status 200 due to customer function error: Exited with code 6. Lambda request id: 9f7c4d24-afee-4ef9-ae14-14e8afcbb712
(a4be7bdd-e53a-409a-b804-28f9129cde0b) Method completed with status: 502

Any clue?
It would be great if the exit code will be 0 and if we can have the possibility to set the response needed by apigw.
Thanks