Lambda was unable to decrypt the environment variables because KMS access was denied

Dear Author,

For some strange reasons only the GET SINGLE TODO ITEM request is not working while all other APIs are working fine (i.e., LIST, CREATE, UPDATE, and DELETE).

I am getting this error, in the API Gateway console.

Reference Example: https://github.com/serverless/examples/tree/master/aws-node-rest-api-with-dynamodb

Endpoint response body before transformations: {"Message":"Lambda was unable to decrypt the environment variables because KMS access was denied. Please check the function's KMS key settings. KMS Exception: AccessDeniedExceptionKMS Message: The ciphertext refers to a customer master key that does not exist, does not exist in this region, or you are not allowed to access.","Type":null}

I am using same ITEM ID in both GET and DELETE methods, the DELETE method works but the GET method throws an Internal Server Error (stack trace as mentioned above).

Please suggest.