Actually, it was declined, but when I called Chase, Chase said it was submitted by Plastiq as a cash advance (not submitted as a purchase) and that's why it was declined! And they told me that if I'd had a higher cash advance limit, it would have gone through and posted as a cash advance, not as a purchase! You earn no points/miles/cashback/anything on cash advances, so why in the world would any FTer want to have a Plastiq payment on their own card show up as a cash advance?

I've sent off an email to Plastiq to try to get them to explain themselves. The link above claimed that Plastiq would warn us if the transaction was going to be processed as a cash advance, but they did no such thing, they only told me that it might be limited to 20% of my credit limit, but nothing about a cash advance. So IMHO this is sneaky and misleading and wrong: Plastiq should be not doing cash advance without saying so (or at least warning of the possibility) and giving me the chance to back out.