On Chargemap there's a closeup of the sign next to the chargers. It says reserved for charging, max 24h, and the charging stations don't need to use the parking meter.
The sign doesn't mention eCarUp at all, instead it says to use the Automat to pay 7CHF for 7h of charging. There's no closeup of the payment machine, but I think we see it fixed to the wall, there are 2 machines, one between chargers 1&2, the other between 3&4.
On eCarUp there's a time component, so I guess it's also a perfectly valid payment method. If the cash price on the Chargemap pictures is still current, you definitely need to use cash, it will be so much cheaper. But it won't stay activated as long. Roaming doesn't seem to be enabled, so there's no cheating the time fee by using a different contract.