What does it take to make a platform like paypal or moneybookers and become a PSP?
I am wondering how I could make something like paypal or moneybookers ( but in small scale) to have a few websites and shops redirect their costumers to complete their purchase by paying there.
I think there must be an API available to them through which they can connect to my payment system. I was looking for some available framework and I came across ZendServer which seems to be an ideal environment for developers to make  applications in PHP. The thing is that most of these websites are already up and running and I need a solution that requires the least possible alteration in their website as possible, so this is us who have to be able to accommodate a wide range of websites using different CMS like drupal, wordpress, joomla and etc. 

I would really appreciate if someone could help me find the best way to achieve this goal, since I have a vague outlook toward how such a thing is done technically.

Thanks alot in advance.
What does it take to make a platform like paypal or moneybookers and become a PSP?
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I am wondering how I could make something like paypal or moneybookers ( but in small scale) to have a few websites and shops redirect their costumers to complete their purchase by paying there.
I think there must be an API available to them through which they can connect to my payment system. I was looking for some available framework and I came across ZendServer which seems to be an ideal environment for developers to make  applications in PHP. The thing is that most of these websites are already up and running and I need a solution that requires the least possible alteration in their website as possible, so this is us who have to be able to accommodate a wide range of websites using different CMS like drupal, wordpress, joomla and etc. 

I would really appreciate if someone could help me find the best way to achieve this goal, since I have a vague outlook toward how such a thing is done technically.

Thanks alot in advance.