Plastiq has a ways to go before being a legit company. The past 2 months I've used my discover card, when I went to make a payment today I got a msg that they are experiencing a "processing outage with MC and VISA cards" and should consider using an amex.
I live chatted (at least they finally got that working) and askes when Discover will be back and working. Their response was that they aren't set up to process discover.
Hmm...