status codes http api gateway proxy

IntegrationStatus - For Lambda proxy integration, this parameter represents the status code returned from Lambda, not from the backend Lambda function. Status represents returned from an integration. For AWS Lambda proxy integrations, this is the status code that your Lambda function code returns.

In your case, status is HTTP 503. A 503 error code is related to the backend integration and if the API Gateway API can't receive a response.

This error might occur in the following scenarios:

The backend server is overloaded beyond capacity and can't process new client requests. The backend server is under temporary maintenance. To resolve this error, consider provisioning more resources to the backend server and activating an exponential backoff and retry mechanism on the client. Then, try the request again.