Razor PartialViewResult yields only the partial view

Question

I'm using Unobtrusive Ajax with Razor. When I return a Partial View, only the partial view content returns on a new blank page instead of in the designated div on original page.

   <form method="post" data-ajax="true" asp-page-handler="Partial" data-ajax-method="post" asp-route-id="JobNum" data-ajax-success="success" data-ajax-update="#panel">
                            
                            <input type="submit"/>
                        </form>

   public async Task<IActionResult> OnPostPartialAsync(string id)
        {
            return new PartialViewResult
            {
                ViewName = "_IndexPartial",
                ViewData = this.ViewData
            };
        }

expecting the result to be displayed in the with id "panel"