Before submitting any ticket please make sure you have watched this video guide:

Please check tutorials at:

If its still not connecting, try to end both apps by using double tap on home button and slide up (on iOS devices) or using task manager on android. After this try steps above again. 

Also try opening Infinite Flight first before opening Infinite passengers. also double check wifi connection. try over mobile data.

If its still not working please raise a support request.