I am trying to find out some technical doc,blog or sample code, which can help me to integrate Squareup API into iOS. I have googled it already, which didn't helped me much. I have the android github code for reference.
I have also found the feasibility of squareup in iOS, as you can check this app: http://itunes.apple.com/us/app/drchrono-emr/id363897223?mt=8
This app has used the squareup, that means, it is available to integrate in iOS.
Looking forward for the suggestion.
Square does not offer an API. [Source1] [Source2]
Their official Github account does have a deprecated (as of April 2012) android api that will not work. I would advise looking elsewhere for in-app payment solutions.
Also keep in mind that in-app payments are a gray area in the iOS terms of service. If you are selling something in the app, it must be available for sale outside of the app as well. Selling items through the app only will have to use Apple's In-App Purchase framework so they get their 30% cut.