I don't fully follow. When you say that he has booked the TGV with Interrail, do you mean that he has entered it as a Trip? If he had made a booking on the TGV he should have a reservation.

If you don't have a reservation yet for Paris to Barcelona on 17 May (which is a Tuesday), then call SNCF ASAP (press #85 for English). If there are still pass holder seats available, they can book them and send the reservation via e-mail. The pass holder seats on the TGV to Barcelona usually sell out in advance.

OR-what rian tells he has done some 100+ times, the rest also: take any-not very late-TGV to PERPIGNan (perhaps still even @ 10€) and use local/regional trains via Port Bou from there=free on pass. Takes longer, gives more to see and thats the true InterRail spirit. Plus that the train in Spain also stops at many more stations in centre-Barca-perhaps thus saving the metro and time for that

Thank You for all your help everyone. We do have the inter rail train booked for Paris Barcelona but it will not let us reserve a seat. It seems seats are full now so may have to try the Perpignan route . I have spoken to someone from trains Europe. Will try phoning SNCF but may be too late. Thanks again everyone.

When you add the journey to your pass it´s “not booked” you just say you intend to use this train. The App is just the “Traveldiary” with the old paperpasses you had to write down each train. With the mobilepass you do it with the Railplanner App

When you have made a Seat Reservation (with Trainnumber, Carriage Number and Seatsnumbers) you are booked on the train.