how to send UDF in Payumoney?

I have an payment link

http://ift.tt/2vHhmpb

i want to send some additional paramerter like

http://ift.tt/2vpg5rq

so that at the response i can get it and i can identify the transaction better. because payumoeny send email and phone number of that person who enters during transction but i want that a person signs up then he is redirected to payment and i recieve a webhook then i update the transaction details in my database.