When working with fixed price season tickets, there are some specific conditions to understand at configuration time, to ensure a smooth operation.
Use case: you want to "sell" complimentary fixed price season tickets for your special guests.
Attention point: if the season ticket is on sale on a ticketshop, your guests will not be able to add performances to their season ticket if the tariff used to sell (the complimentary tarif) is not available in the product profile. But if you add it, then your season ticket will go on sale at this complimentary tariff !
Solution: you need to configure a different season ticket for your complimentary guests. Just duplicate your season ticket, set a 0.- price for a complimentary tariff. And simply do not sell this special season ticket on the ticketshop. When a season ticket is not on sale on a particular ticketshop, there is no specific condition on the availability of the tariffs.