Error converting data type nvarchar to bigint but I already use Convert.ToInt64

Question

I have a input textbox in my view what only accept number:

<input asp-for="order" class="form-control" MaxLength="120" type="number" />

Order is a bigint column in the database table.

Then in the controller I write the following code:

parameters.Add(new SqlParameter("@order", Convert.ToInt64(obj.order)));
parameters.Add(new SqlParameter("@extra", obj.extra));

var objList = _db.Database.ExecuteSqlRaw("update @order, @extra", parameters.ToArray());

But I keep getting the same error whatever I try to change. The error is:

Error converting data type nvarchar to bigint

Also when I just put a number in the SqlParameter it's not working like:

parameters.Add(new SqlParameter("@order", Convert.ToInt64("10000")));

The update stored procedure is just very simple:

(
    @extra nvarchar(MAX),
    @order bigint
)
AS
BEGIN
    UPDATE dbo.table
    SET extra = @extra 
    WHERE order = @order
END
RETURN 0