C# Razor partial view using an iFrame returns dictionary error "`1" and "`2"

Question

I am attempting to load a partial view into an iFrame and receiving the below error. When loading the same partial not inside of a iFrame, there is no issue. Looking for any information as far as what the "`1" and "`2" means in the error message.

<iframe src="@Url.Action("GetFooPartial", "Foo")"></iframe>

        public ActionResult GetFooPartial()
        {
            foo<fooOptions> vm = new foo<fooOptions>();
            return PartialView("~/Index.cshtml", vm);
        }

The model item passed into the dictionary is of type 'foo`1[fooOptions]', but this dictionary requires a model item of type 'foo`2[fooOptions]'