PHP graphql $response->getBody()->getContents() get "debugMessage":"Expected a value of type error

Question

I am using PHP guzzlephp to query the data. Got the "debugMessage":"Expected a value of type error. The error comes from $content = $response->getBody()->getContents(); looks like it's not able to parse the response body. The wired thing is if the response is "laneStrategy": "COST": it will be parsed well, but if change to others, it throw the error. I have a enum defined like this:

class LaneStrategy {
  const COST = 1;
  const SPEED = 2;
  const ORCHESTRATION = 3;
  const STANDARD = 4;
}

correct response:

  {
      "lane": {
        "laneID": 20234,
        "laneStrategy": "COST",
        "stops": [
          {
            "sequenceNumber": 0,
            "node": {
              "nodeID": 200
            }
          },
          {
            "sequenceNumber": 1,
            "node": {
              "nodeID": 100
            }
          }
        ]
      }
    }

When the response contains other type for laneStrategy except "COST" it will throw error message: "errors":[{"debugMessage":"Expected a value of type \u0022LaneStrategy\u0022 but 2 received In the error message the 2 is exactly the number defined in enum, but I just don't get it why it throw the error using other types? Can anybody know what possible wrong? Thank you