First, don’t underestimate that "local" support.  My two books I’ve funded was done almost entirely through personal contacts that I rallied to the cause through various....means :-)  For now, starting out, that local base is your foundation.

Second, I’m not saying go recruit with the message "buy my book and you have to go jump through all these steps!"  It’s hard enough already, that would complicate things.  I would save the suggestions for stuff like this ONLY for people who are wary of using their own card information and express that as the only barrier.

did some research.  Here are some suggestions:

Ask your bank to set you up with a secondary account for online purchases, and keep only a small amount in that account. The account would need its own ATM card, with its own credit card number. Just make sure this account lacks overdraft protection; you don’t want money moving automatically from your real account into this one.

Buy a Visa Gift Card online from an official retailer.  Con: not reloadable so when it’s done it’s done.  One of many example retailers: www.giftcards.com/visa-gift-cards  Additionally, in Germany you can buy gift cards at these locations and more:  Gallerian, Kaufhof, Karstadt, Douglas, H&M, etc.

I would need to do more research into it, but you could look into getting a virtual credit card, like VCPay.  Here’s an article from a South African explaining how he is using it: https://toughnickel.com/personal-finance/VCpay

Another possible method that I would need to test to see if it can be used like a credit card is Paysafecard (https://www.paysafecard.com/en-us/products/)  I did a search using my village’s postal code and found vendors in my village and the two neighboring ones. 

Finally, in my research I found Global GCash Virtual Pay, which has a lot of little nice benefits that can be used.