You can get e tickets (and presumably PRT) to from/the Marshlink stations (run by GTR) if the other station is enabled and the journey doesnt invove cross London . Ive had several e tickets from Appledore (kent) to Fratton for instance. You cant get tickets to SE stations Hastings, St Leonards, Ashford Int., but the Appledore to Fratton ticket is valid on Southeastern trains via Tonbridge and the guards have always accepted them without comment in my case. I believe that West Coastway stations are progressively being equipped with barcode scanners but havent used rail down there since the pandemic. Ive never actually had a barcode scanned anywhere on a train on GTR obs just look at the phone etc to see whereyou are going.