[Solved] ASP.Net Error: Unable to cast object of type System.TimeSpan to type System.IConvertible

Hi Guys,

I'm try to calculate due date between two date, but I can't find how to do that in best way in C#.

I'm found the references code in VB and then I'm trying to translate that code to ASP.NET C#.

This Code in VB

'find the due date based on installments to ???
DueDate.Text = DateAdd(DateInterval.Month, Val(InstallmentsTo.Text), DateValue(RentDate.Text))

And this code I'm trying to translate in C#

    private void SearchDueDate()
    {
        System.DateTime PaymentDate;
        System.DateTime RentDate;
        System.DateTime DateNow;

        DateTime InstallmentsTo;
        InstallmentsTo = Convert.ToDateTime(txtcicilan_ke.Text);

        RentDate = Convert.ToDateTime(txttgl_pinjaman.Text);
        PaymentDate = Convert.ToDateTime(txttanggal_pembayaran.Text);

        txttgl_jatuh_tempo.Text = Convert.ToDateTime(PaymentDate - RentDate),InstallmentsTo.ToString("yyyy/MM/dd");
    }

When I the code running get this error

Unable to cast object of type 'System.TimeSpan' to type 'System.IConvertible'.

RentDate = 2021/06/01 //yyyy/MM/dd

PaymentDate = 2021/07/01 //yyyy/MM/dd

InstallmentsTo = 1

Any help could be appriciate.