Unable to derive mutation in Hasura

Question

I am having trouble deriving a mutation in a Hasura table I have. This is my mutation:

mutation MyMutation {
  AddReview(body: "fear not, it will work", id: "xeZiZnx61MFWDxfhgAu-gQ") {
    affected_rows
  }
}

However, when I try to derive an action, it gives me the error message: Name "typename" must not begin with "", which is reserved by GraphQL introspection. I am not sure what I am doing incorrectly. All the permissions etc for the table are correct. Did anyone else have this error? Not sure if it is also a Hasura bug...