SBB acts as an intermediary for the sale of Parkingpay tickets. The conditions stipulated by Parkingpay (Digitalparking AG) apply. Extract from Digitalparking’s FAQ: “As a rule, the same tariffs apply for the parking meter/cash register. Where explicitly indicated, surcharges are applicable on the parking spaces of specific operators (e.g. Geneva) and/or for the use of certain Parkingpay functions (e.g. individual charges on the means of payment).”
The actual costs are clearly indicated for the user at all times in the P+Rail app.  pakingpay.ch Link opens in new window.