@primary directive for 1-Many Fields throws odd error

[jsimnz]

Context:

type Todo{
    title: String!
    userName: String!
    isSeen: Boolean
    todoUser: [TodoUser]
}


type TodoUser{
    isVerified: Boolean
    name: String! 
    age: Int
    todoCount: Int
    todo: Todo @primary
}

Resulting error:

duplicate field. Name: todo