Express Checkout C# ASP.NET Core APP Sandbox error, 400 Bad Request

[Mvce]

I can see details about the payment in the alert screen and the PayPal Sandbox account receive the payment according, but I can't capture these details in my ASP.NET Core 2.1 code to record in the database. Here the code I used: https://developer.paypal.com/docs/checkout/integrate/

    public async Task<IActionResult> OnPostAsync([FromBody] string orderID)
    {
        Console.Beep();
        TempData["Message"] = "Pagamento Salvo";
        var user = await UserManager.FindByIdAsync("10");
    }