I'm using the latest 4.1.2 for testing this out.
I don't understand what you mean, when you say "done automatically by WHMCS". You mean that WHMCS will "automatically" adjust the billing accounts when Paypal notifies on IPN about the changes in subscription? I'm not looking for having the functionality this way.
What I was expecting is that in the My Services list view, the customer will be given a separate button next to the view details button, to "edit" the subscription values, such that they can change the payment schedule, or the quantities in the configurable options. On changing of the values, WHMCS would raise an invoice for the differences, and provide a "modify subscription" button on the Invoice, instead of the subscribe or the checkout buttons that appear currently.
If this functionality is "automatic" in the above way, then it's much less convenient, yes? I will have to create a separate screen/template myself, where I will have to create the modify button to send the customer's browser to Paypal with the new values, just so that WHMCS can update itself with the modified subscription when Paypal callbacks with IPN. This will get incrementally difficult for me, because I'm thinking there'll be a lot of code to be written here, using the WHMCS API, even if this is possible at all !
I'm not really interested in changing the payment schedule right now, but this will also become a requirement for me in a different product that I will also be selling through WHMCS. If I can get my head around the modify subscription functionality at all, of course!
The Wiki page on Paypal (http://wiki.whmcs.com/PayPal) is quite non-ambiguous about the modify subscription functionality : "By enabling Modify Subscriptions, customers will be given the option to create a new agreement or modify an existing one when going through the subscribe process."
What I want to do is to "modify an existing one". Any ideas?
The only other possible case where this Modify Subscription option will be given to the customer user, that I can think of is at the end of the payment schedule period of a month. I see no way to set up a daily subscription, and I am unwilling to wait a month just to see if any buttons start appearing!
Thanks for responding, ChrisGooding, I really, really hope that solving this problem is possible. WHMCS is pretty much the only software that is even close to achieving this for me, and the other functionality is stellar as well.
I really need to get this modify subscription thing working, though.
-Dhiraj.