I tried to reserve seats to France - Spain train. Unfortunately reservations for trains between France and Spain are only on paper. The system calculates that it takes more than 4 weeks to deliver tickets to Finland. So I called directly to SNCF and they could have made the reservation, but they don’t accept visa payments from Nordic countries so the reservation was impossible.
They advised to contact Interrail again. Which is a dead end cause only paper tickets and delivery is impossible.