My first purchase with the card last autumn was a ticket on Priceline. I canceled the ticket within 24 hours, but the $325 credit kicked in, so my balance owed was -$325.

Not really a way to “cash out” per se, but you could essentially spend the $325 on anything else that billing period and have it covered by the credit. I don’t know about calling and asking for a check to be sent for the credit balance, because they might realize it kicked in for nothing...