It seems clear that the only currently-supported ways for the general public to donate are via this DonorBox form (which only accepts U.S. postal codes), via PayPal, or via Bitcoin. However, it would be great if ISRG could get DonorBox to accept credit card donations from other countries, as well as publishing bank transfer details for international donations. Maybe some of our colleagues from ISRG can look into how difficult this would be.
I believe you can also use PayPal for a one-time credit card payment, although they will try to upsell you to using their services on an ongoing basis and might not allow you to use the same card or e-mail address for future payments without setting up an account.
@linucks, thanks for your interest in donating and for not giving up when the donation form didn’t work for you!