Quantity editable on hosted page created via API

Quantity editable on hosted page created via API

Hello.
I started integrating my application with Zoho Subscriptions and I really like it so far.

I need some help with the following issue.

I want the quantity for the subscription to be editable.
If I use the basic hosted page url, I can correctly edit the quantity.

But I don't use the basic url, I create a new one programmatically for the user, so they don't have to input their account info again, and with this generated hosted page, the quantity field is locked. Why? How can I get it to work?

I can pass the quantity explicitly while creating the hosted page, but still, once the user is on the hosted page, they can't change it.

Thank you