[Ted S]

Payment APIs can be fairly tricky to implement as you have to match up how they authenticate with vBulletin's needs and while the code is built to be modular on VB's end, even a small difference in how the API functions can become a real pain... like if they don't report back actively when a sub fails.

The process [what you have to build hooks to make work, vBulletin handles the interface]:

1- The user submits payment either through your site or by being passed off to a third party payment page
2- Automatically reading the response back and updating appropriately. This seems instant but it's actually a call after everything is confirmed / denied.
3- Updates to charge again / report back a failed charge for recurring subs. Not required but manual renewal is never 100% so doing it is generally smart.

From the page you linked too it appears you can do the second part [get notified when a subscription is approved] but will need a paypal-like setup to create an unapproved subscription, jump the user to their payment page, and then back to you when they finish or abort. It's not terrible but it's also not as simple as mirroring a seamless provider's to use another set of API calls.

If you can't hack php decently you'll need help... or roll up your sleeves and keep changing things until you start to get it.