Make sure iTunes is the most recent update and restore your iPad. Then try again.
Before proceeding, you should be aware that the use of Popcorn Time and similar services may be illegal. Much of the content of these services is copyrighted material being shared and downloaded without permission from the owners. The use of these services will often result in a violation of copyright depending on what you watch. If you still choose to use the services you do so at your own risk and it is advisable to follow the law.