Hi everyone, 

I have the following scenario:

I created a flow that i placed on a public SF site. Basically, It allows for people to select an event and then register for it. "Event" being a custom object. They can register as Exhibitors, 3 Day Attendants and / or Full Weekly attendants, and each time a registration is made, an "event registration order" (custom object) is created, which will link up the type of attendants they are registering as with the event they are registering for. Basically my Salesforce relationship modeling is working solidly .  

The next step is the following:

I have to, once the registration (and order has been made. send them to a payment portal that we built in-house. The problem that I have, is that I want to direct them to our portal, but also send information regarding that order (cost, reference etc) to that site as well, so that the person that built the portal can do the processing. 

Once the customer has paid successfully (at our payment portal) , I want to re-direct them to the second flow that I created, which will check the incoming variable references, and change the order  status to "Paid". 

Question:

Firstly, I know about the "Finishing" flow function, that will redirect the flow to a url, but how can I make that dynamic so that it will for each flow add variable data to an url? I.e. it must build a url dynamically and then redirect it to that url? The payment portal must be able to receive values so that it can send a response to another flow once the payment is successfull. 

Secondly, i know that you can, within salesforce, do calls to flow and put incoming variables in the call (for example) /flow/flowname/?variable1="value"?variable2name="value"

BUT how do you do the call when the (called) flow is now placed in a VF page, on a site? For example,   www.url.com/registration is the url, do i now do it like previously and just go www.url.com/registration?variable1="value:" - will that work?

Really would appreciate the help

Regards,

Stadler van Zyl (new to SF)