# Almost not a technical question

**URL:** <https://www.ruby-forum.com/t/almost-not-a-technical-question/187303>\
**Category:** Rails\
**Created:** [April 21, 2010, 2:05pm UTC](https://www.ruby-forum.com/t/almost-not-a-technical-question/187303 "2010-04-21T14:05:47Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![gregm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/bc79bd/32.png) [@gregm](https://www.ruby-forum.com/u/gregm)\
**Post date:** [April 21, 2010, 2:05pm UTC](https://www.ruby-forum.com/t/almost-not-a-technical-question/187303/1 "2010-04-21T14:05:47Z")

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Hi,  
I would like to develop a paying system like [Groupon.com](http://Groupon.com) does. For those  
who don’t know about groupon, you can purchase coupon only if the coupon  
as been sold “n” number of times. But when you pay you are charged only  
if the limit number of people has been reached.  
This means then save somehow your credit card number somewhere and  
charged you when the sell is done.

My question is how, where do they do their paying thing?

Greg

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**Author:** ![gregm](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/g/bc79bd/32.png) [@gregm](https://www.ruby-forum.com/u/gregm)\
**Post date:** [April 21, 2010, 4:43pm UTC](https://www.ruby-forum.com/t/almost-not-a-technical-question/187303/2 "2010-04-21T16:43:23Z")

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On Wed, Apr 21, 2010 at 5:05 AM, Greg Ma [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> But when you pay you are charged only  
> if the limit number of people has been reached.  
> This means then save somehow your credit card number somewhere and  
> charged you when the sell is done.
> 
> My question is how, where do they do their paying thing?

I would imagine most if not all payment gateways (e.g. [Authorize.net](http://Authorize.net))  
allow a “Authorization Only” submittal; the card is only actually  
charged  
with a subsequent “Prior Authorization Capture” using a transaction id  
or some other token, which means there’s no need to retain the actual  
card data on the site (a very good thing!).

## HTH,

Hassan S. ------------------------ removed\_email\_address@domain.invalid  
twitter: @hassan