I would like to know if is possible to create a system that pay/receive automatically based on what is happening in the site.
I would like to know after a payment that it has succeeded or not in order to activate the service.
I don't have a business so what is my best choice? (country: Portugal)
Example of what I would like is 99design.com (not exactly how it happens):
What I Really NEED:
This is actually some what of a technical question not really a 'start up' question.
I'm not sure what countries PayPal works in, but whether you have PayPal standard or Pro you can achieve what you are looking to do.
With PayPal Standard there is a concept called IPN Instant Payment Notification. You can essentially call a web service or page back on the originating website once they finish the transaction on PayPal. Once IPN calls back to your website you would need to have custom code/logic to mark in your database that the contest has been paid for.
If you were able to upgrade to PayPal Pro in your country you can do a lot of this without the user ever having to go over to the actual PayPal website.
You would essentially pay commissions out to people by sending them money via PayPal to their email address.
There are probably content management systems or e-commerce systems that may be a good fit for you to automate some of this. It's possible that Drupal 7 and Drupal 7 commerce could achieve this without much programming. (But I'm just guessing).
Typically this stuff is custom coded for a specific need.
Regarding your update: