Variable PHP Sessions in iOS APP not working


We have build a webview APP for both Android and iOS. We have the APP already in the Google Store working fine and with no problem.

But, with iOS we have the next problem: Every time a page is loaded, any $_SESSION variable we have, is deleted, like is refreshed every page it loads. So, we can access to the first page of the APP, but when we log in, it does come back to the main page without any session var. stored. Is there any way to store this variables within iOS or is there any way to handle this?

Thanks in advance.