Jet2 gave me this info when we were flying back with them this July:
'Mobile boarding passes are now available in the Jet2.com mobile apps on iOS and Android for the majority of our destinations. To find out more about how to check in and get your boarding passes through the app, please watch our handy video guide
Unfortunately, there are some airports that don’t accept mobile boarding passes at the moment. You will still be able to check in online and get a boarding pass on your smartphone. However, if you are travelling to one of the following destinations, please still go to the check–in desk at the airport. There will be no charge if you have already checked in online or have pre-selected airport check in:
Antalya (AYT)
Bodrum (BJV)
Dalaman (DLM)
New York (EWR)'