How can I pre-populate description field in custom-donation paypal addon

I explained the problem in screenshot.

If you want to pass a specific amount directly in the donation field, then you can follow this guide: http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field.

If you are referring to the "Payment Purpose" field, unfortunately, it is not possible to prepopulate via URL parameters, it is a fixed text or static.

Let us know if I understood your concern correctly.

Yes I understand thank you. But I think that function is missing in jotform. Because when I using gravity forms I was able to do that. So I find a solution maybe other people who struggle with that cen benefit from it;

1. Create all of your products as a single product and create urls like example.com/order?myproduct[][id]=1001

2. In css editor make display:none; where is product file.

3. Create 2 text field and make them read only.

4. In css editor make that fields borders invisible by writing 

{

    border : 0;

    box-shadow : none;

}

5. add conditions for your each product like if product==1001 populate first text area with product information and populate second area with price information

so its not a logical way to do that but I need jotform because I dont want to use php anymore :D