How to Use OCPP Server in AWS lambda using webSockets API and Raspberry Pi acts as OCPP client ?

If I remember correctly, the URL that you need to use for OCPP has a specific structure which doesn't work with the way API WebSockets URLs look like. One way to overcome this is by using a CloudFront distribution in front of you API, which will rewrite the URL using CloudFront functions, before forwarding to the API in the backend.

You could use the AWS API Gateway service as a proxy to your Lambda function. This would allow you to call the Lambda function from your Raspberry Pi. You would need to create an API method in the API Gateway to handle the OCPP requests, then map it to the specific Lambda function that you have created to handle the OCPP protocol.