There are basically two cases in which you cannot add certain tickets to your shopping basket:
Tickets for an event
If you cannot add the selected number of tickets to the shopping basket for an event, there are probably not enough tickets available.
If 5 or fewer tickets are available for an event or an event category, this will be displayed:
Tickets for several events
Tickets for different events can of course also be added to the shopping basket.
However, it is currently not possible to add tickets from events with different currencies to the shopping basket. So if you already have tickets with a price in CHF in your shopping basket, you cannot add tickets in euros.
To be able to buy tickets for both events, complete the purchase process for one event. Once your shopping basket is empty, you can buy tickets for the second event.