How did you get from drawing software to payment gateways?
From the KDE mailing list that it's linked[1] where the article mentions why they didn't go with Kickstarter
[1]https://mail.kde.org/pipermail/kde-community/2018q4/004976.h...
It seems like Krita uses that one: https://krita.org/en/donation-analytics/
It's not mentioned on the Donate page itself though, so I'm not sure how they found that out in the first place.
Use the source, Luke!
[1] https://www.mollie.com/en/