Been developing a site for a friend which will be membership-based and use a billing company to process payments.

I've been using this very helpful forum to investigate the best billing companies but I do have a technical question with regards to the interface between the billing co. and the trading website:

Can you tell me - how, after payment is made at the billing company's site, do a new member's detail get entered into the trading site's database?

Is it a case of connecting from billing company to a php creation page (which we'd have ready) on the trading site to then enter new member's details?

OR...Do the billing companies' require direct database connection to insert new members details immediately after payment? Would this not be a security risk?

It's a perplexing little logistical conundrum the inexperienced that we've just come across as we develop the membership database in mysql and php.

I'd appreciate someone with the experince and knowledge to put me on the definitive right tracks as we set up to launch the business.

Thank for your interest, hope you can help.