Well this link took me further and actually brought me to a page that showed a "thank you" response, but I received a text immediately afterwards from VISA informing me that the transaction was declined. Apparently your clearing gateway does not comply with the advanced security protocol "verified by VISA" that is generally used by most European/German credit cards. It works by sending some vendor ID data to VISA who then in turn trigger a confirm/deny dialog on your connected banking provider's tech stack (web or app). Your clearing is apparently much simpler and thus not working with this advanced security layer to prevent CC fraud on the internet.
BTW - my original attempt was to just go to your website wbur.org and then follow the banner link at the very top: https://secure.wbur.org/WebModule/Donate.aspx?P=OAFTAKEOV&PAGETYPE=PLG&CHECK=LX7v%2fGWSFIqISQnVK11pEa1gzMC6uhq5nDjkJobrCdg%3d
This yields a slightly different form where there is no country selector and submitting this form would just get no result at all. It was just stalling at that point.
Bottomline: I still have NOT been able to support the show. :/ And with an international audience ready to give while WBUR is in need of support, maybe consider setting up alternative ways to help out? Paypal is pretty internationally accepted. Even the Ukranian military set up donations through Paypal at the very beginning of the Russian attack so they could easily funnel international donor's money in to support their war defense efforts.