I am trying to buy Digital Atelier through Gumroad + PayPal / Debit Card, but it will not work.

If I try to pay using PayPal (with sufficient saldo) it keeps asking me to connect a Credit Card, which I neither have or want.
If I try to pay using a VISA Debit Card, Gumroad complains that it cannot verify the card so I cannot use it.

(I had this problem before on Gumroad, while itch.io worked fine using the same PayPal account.)

Is there any other way to buy the Digital Atelier resource pack? Thanks!

No, there isn't any other way, and since we started the sale, about a score of people have managed to buy Digital Atelier, so it isn't broken for every one. If you paypal foundation@krita.org the money, and mail foundation@krita.org the proof you've done that, I will send you a link, though, personally.