On which lines is the ticket purchased via a Budapest Pay&GO device valid?

The airport shuttlebus single ticket purchased on board the 100E Airport Express is valid only until disembarking on that bus and cannot be used to transfer to other lines.

As with single tickets purchased through other sales channels, a single ticket purchased on the Budapest Pay&GO device at the station entrances of metro line M1 is valid for one ride if going in the direction of Mexikói út terminus (for example, to Hősök tere or Széchenyi fürdő stations), or for a transfer journey if going on line M1 in the direction of Deák Ferenc tér, in which case the ticket is also valid on the entire length of metro lines M2, M3 and M4, travelling in one direction with transfers between lines, but no stopovers and return trips are allowed, and the journey must be completed within 80 minutes at the latest.