Greetings all. Zen newbie here, so hopefully I'm putting this in the right section of the forums. I'm looking for a little guidance.

I have a site going online soon using Zen that sells some paper products. The site also has a Membership component (free subscription) that's separate from so that people can use some free software I've developed to print stuff on the paper they buy. My goal is to set up something in Zen Cart that will automatically create and populate their username/password for them at the end of the paper purchase via the shopping cart, rather than force them to go through a second registration process. Using the same login/password they set up during the Zen account creation to keep things simple.

Looking at the API Tutorial I'm sure this can be accomplished and it might even be easy to do by creating a new class. I'm just not sure what to use as a trigger for fire a new php routine. What I'm looking for is the Notifier to check against to see if an order process has been completed, with payment approved, at which point I can then check against the (separate) membership database to make sure an account for the person doesn't exist and create one if needed.

There are a few that might be what I'm looking for, but I'm not clear on what each does or when it's fired. eg NOTIFY_ORDER_PROCESSING_STOCK_DECREMENT_BEGIN or _END, which I assume wouldn't fire until payment had been confirmed, or NOTIFY_ORDER_PROCESSING_ONE_TIME_CHARGES_BEGIN or possibly any of several CHECKOUT choices.

Has anybody done something like this before? Any hints or guidance as to which notifier would be the best to use? Or as an alternative can anybody point me to the file that causes the Thank You page to load after purchase has been completed?