Google HomeGraph API: "Request Entity Not Found" error when reporting device state

Question

I'm working with the Google HomeGraph API to report the state of my smart home devices. However, every time I try to report the state, I receive a "Request Entity Not Found" error, even though I've verified that the agentUserId and device ID in my Report State request match those in my SYNC response.

    {
      "requestId": "65e8be46d4ff6",
      "agentUserId": "5",
      "payload": {
        "devices": {
          "states": {
            "2": {
              "online": true,
              "openPercent": 70
            }
          }
        }
      }
    }

I receive response

    {
        "error": {
            "code": 404,
            "message": "Requested entity was not found.",
            "status": "NOT_FOUND"
        }
    }

I've double-checked the following:

The agentUserId matches the value provided in the SYNC response. The device ID ("2" in this case) matches the ID used in the SYNC response. The access token used for authorization is valid and has the https://www.googleapis.com/auth/homegraph scope. Despite this, I continue to receive the "Request Entity Not Found" error. Has anyone encountered this issue before, or does anyone have suggestions on how to resolve it?