The barriers at City Thameslink are advertising mobile tickets.
It appears you can get e-tickets from City Thameslink to:
St Albans
Luton Airport Parkway
Luton
Bedford
Stevenage
but not to:
Gatwick Airport
Flitwick
Hitchin
Peterborough
Harpenden
Leagrave
It appears you can get e-tickets from City Thameslink to:
St Albans
Luton Airport Parkway
Luton
Bedford
Stevenage
but not to:
Gatwick Airport
Flitwick
Hitchin
Peterborough
Harpenden
Leagrave