Cannot create Commitments

[vcuculo]

Trying to create a commitment in response to an offer, as follows

mutation {
  createCommitment(
    commitment: {
      action: "transfer"
      provider: "01F3MHQ0KWJC7M19B1E8BXVY46"
            receiver: "01F7XMMHQ81HQ6DA10XFN24B2E"
            resourceConformsTo: "01FE4094Y6J99MEDWXBXQCAJF8"
    }){
    commitment{
      id
      provider {
        name
      }
      receiver {
        name
      }
    }
  }
}

returns in

{
  "data": {
    "createCommitment": null
  }
}