Hello AYBERK,
You can try the API in Postman or swagger and check whether getting response there or not.
error incomplete may be due to $latestHttpResponse/Content is empty or not in the expected format.
Please ensure header in your REST call is set to application/json or the expected content type. If you will be able to get content in post man, then you can use the same setting in REST call.
In the given example in your question first try to remove $latestHttpResponse/Content part and then you can confirm it is due to content.