Error: Argument "data" is not a valid Document. Input is not a plain JavaScript object

In case some else bump into the same issue, the solution is to simple use Json to instantiate the object, like this:

var myDoc = {
        Public: {
            Name: "Jonh Doe"
        }
    } as MyDoc; //keep type to still get typescript compiler validations

I did something similar:

var myDoc = <MyDoc> {
    Public: {
        Name: "Jonh Doe"
    }
}

It is semantically the same, I just think it is a bit cleaner.

I had same problem, in my case I'd forgot to add Content-Type:application/json to my header when sending request, and then the object was treated as string and I got that error.