On one hand, this shows how important it is for paper cash to have first-class citizen status when it comes to legal tender.
On the other hand, how does the largest single currency zone in the world not have its own debit card settlement system? The Germany-only Girocard appears to have been mostly phased out, and doesn't work outside Germany unless it's co-branded with MC/Visa. Same with France's Card Bancaire. Besides that, 39% of online purchases in Germany are made through PayPal or MC/Visa.
[0] https://stripe.com/en-ca/resources/more/payment-methods-germ...