Note that the very latest version of the App has a fix for this.
Get the latest version the app store Click here for the latest version released 23rd Jan
If your device is Jailbroken you will not be able to buy a full plan and it will fail.
If you purchased / upgraded to a full plan but when you try to move forward through the plan you keep on getting the 'buy plan' page, it may be that your download was interrupted.
You will not & cannot be charged twice for content that you have already purchased.
Go to Downloads on the menu. If it does not show 100% then click the 'i' icon and download the content by clicking restore.
Please ensure that you have enough space on your device.
Due to the amount of video content in this app, it requires extra space. The intial app download is around 170mb and it requires an addition 90mb for each plan (approx).