There are plenty of options to pay in the PSI restaurants and cafeterias. Of course cash is accepted (CHF and EUR) as well as all major credit cards (VISA, Mastercard, American Express, Diners), Giro/Maestrocards, Swiss Postcards, Apple Pay, V-Pay and Twint.
In addition there is the comfortable option to upload money to your PSI badge for payment in the PSI restaurant and cafeterias. For that purpose you can use the machines in both entrance areas of the PSI restaurant OASE (PSI East, cashless) as well as the Cafeteria Time-Out (PSI West, cash (CHF) only). The next ATM is located in Villigen.
Only with the PSI badge you can pay at the vending machines in the Cafeteria Time-Out during the weekends and out of office hours.
Remaining assets on the PSI badge can only be refunded during opening hours at restaurant OASE and cafeteria Time-Out. Please take that into account in particular if you plan to leave on weekends or early Monday mornings.
For paying your bill in the guesthouse please have a look here!