Thanks for your report. Interesting that JCB cards automatically refer to it as the "Discover Network" when using for online payments stateside, yet rejects it later.

I assume the programming on the processor is like "if card number is between 3528-3589 process as Discover" while on Discover's side it's like "3528-3589 card number received through Discover Network, 3528-3589 = JCB, we do not accept online payments from BINs under this range." (using the data from Discover's own PDF file)

Perhaps the number of JCB cardholders in the US is so small (and JCB cardholders in the US likely to be those that use them at live retailers and merchants and hold alternative cards anyway) it's one of those that "fall under the cracks" when IT guys tries to test them it out.

Considering that JCB customer service is good, you might want to write up your "success/fail" report to JCB. It won't change overnight, but it would provide good feedback to see how JCB can strengthen their partnership with Discover for online payment solutions (and reciprocally perhaps, Americans in Japan can use their Discover cards for online payment solutions in Japan through the JCB network)