I'm referring to these 11 vouchers for CHF 33, where 1 coffee is free.
You can only get them in the M-Restaurant for cash - and fortunately (but by no means everywhere) at the information desk. There, at least as a Postcard holder, I can withdraw CHF 100 in the first step and pay with it. The employee then fetches a container in the second step, takes out a voucher booklet, puts CHF 33 in the container and gives me back the return money of CHF 67. A little complicated - but at least it explains the procedure for paying in cash (different cash boxes)....
It's more complicated in the restaurant and I've experienced this in various places:
1) I go to the cashier with my coffee, 100 CHF in my hand, coffee already typed in, I want these coffee vouchers for 33 CHF and to pay with a voucher.... Not possible, already typed in, vouchers stupidly in the cash register, I first have to pay for this one coffee (this is also possible with a credit card) and in a 2nd operation (when the cash register is open) I can buy these vouchers - but only in cash. I understand, that's why in other places they have these vouchers stuck underneath the till....
It's kind of weird for me: 10 coffees ^I have to pay cash - I can buy a single coffee with a credit card... and as a regular card payer, I buy 10 coffees precisely because it looks so stupid to use my credit card for a single coffee ;-)