You can't use that from a Rule Based action on Dialler. As this is the only way to trigger a data action it only uses inputs and has no way returning the output form an action back to the dialler so any conversion is not returning its result.
If you can't accomplish what you need with only configuration of a data action, the recommended approach is to create a middleware endpoint that can do what you want and exposes a REST endpoint that the data action can call. This is commonly done using API Gateway and a Lambda function.