Get detailed error messages from AWS API Gateway Request Validator

UPDATE:

This is now possible with gateway responses. Setup a BAD_REQUEST_BODY gateway response with the below template:

{"message": "$context.error.validationErrorString"}

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(Developer on API Gateway)

Unfortunately, this is not supported right now. We are actively working on fixing this issue, but I can't give you any specific timelines by when this could be supported.

Since API Gateway developer had answered the question, I still want to add some tips for you, maybe it is helpful and that can be an accepted answer!

For your question, in fact you need to active the cloudwatch logs for api gateway, with that, you can get more logs than you have before.

Let me know if it included the details for Request Validator

This aws document - How do I enable Amazon CloudWatch Logs for APIs I created in the Amazon API Gateway? gives the steps on how to enable it.

But I prefer to go with this document API Gateway and Lambda Logs, which give the screenshots to follow up easily.

In your api gateway, you should see this is enabled.

Access the API gateway several times, go through the log group which is named as:

API-Gateway-Execution-Logs_{rest-api-id}/{stage_name}

Which has more details than the information you have as Invalid request body and others, such as {"message": "Internal server error"}. It is very useful feature, that save me a lot time troubleshooting serverless and api gateway issues.