I'm using a custom form (created in Gravity Forms on my Wordpress site) to collect a lot of custom information before I redirect them to my Zoho Subscription hosted page.

I don't want my user to fill up his name, phone number and email again on the hosted page. I also want to be able to pass a value to a subscription custom field (which is a unique key to correlate the subscription and its corresponding entry in Gravity Forms.

I tried passing the data as parameters like... 

https://subscriptions.zoho.com/subscribe/1e7d3fb6c1637d77184c1dcc0ce42db16a2bba0f6b053217afe8ded60e8a6aa6/Small ?first_name=Abhishek&last_name=Agarwal&email=abhishek@email.com

But it does not seem to populate. I do not want to use API because I have no development experience and would not want to engage a developer for just this last leg of my website setup, which should be seemingly simple.

How can I get this done? This is the only problem that's keeping me from using Zoho Subscriptions for my business. I'm all set otherwise!