Lambda integration response template mapping

Trying to map the lambda output to a template such that the aws gateway output matches the expected output.

For example
Lambda Output
“statusCode”: number,
“body”: string
"headers": {
“key”: “value”


Attempting a response template in serverless.yml, not working as expected.
template: $input.json(’$.body’)

All examples I see reference $input ( although this is the output ) and not sure if that is correct.
If not what are my options other than $input for response template mapping.