One of my friends tried to do a donation to wikipedia after following a banner on wikipedia.org (either enwiki of frwiki). She was redirected to Wikimedia CH donation page and tried to "order a pre-printed payment slip". After submitting the form, she got a blank page, with no indication that the order was received. One week after, she did not receive the payment slip by post. The same thing happened to her around 6 month ago. Note that I tried to order a payslip as well and I did not have any issue (the payslip has not arrived yet, but I got a confirmation). I know, this isn't much to go on...

It looks like the payment slip order is managed by Wikimedia CH, I'm not sure if they follow issues on phab.