Guzzle returns stream empty body instead of json body

getBody() returns a stream. If you want to get all the content at once you can use getContents() method and decode json while at it (if you need to)

$payload = json_decode($response->getBody()->getContents());

Further reading - Guzzle Responses

If $response->getBody()->getContents() doesn't work for you, try:

$response->getBody()->__toString();

As mentioned here, sometimes getContents's stream pointer is already at the end of stream and then it returns empty response, but __toString resets it by default.