tl;dr – You want to cancel your flight for a full cash refund. If you can wait it out a bit more, you might get lucky.
Here’s the scenario. You purchase an airline ticket in cash (not a redemption) and then later on, before you’re scheduled to fly, you realize you need to cancel the ticket. You’re well past the initial 24 window (whereby you can receive a full refund on most US based airfares via the DOT), so your best option is to receive travel credit from the airline, to be used on a future reservation.
While travel credit isn’t terrible (assuming you have future plans to fly that carrier), if luck is on your side, you might still be able to cancel for a full refund if this one scenario happens.

If there’s a schedule change to your itinerary of more than an hour, some airlines stipulate that you can then cancel for a full refund. That change can be to the departure or arrival time, on any leg of your trip. So if you booked a round trip ticket and the time of your return flight changes by more than an hour, that should qualify. If only one of your flights on a multi-connection one-way itinerary changes by more than an hour, that too should qualify.
I was making a change to a flight I booked with Alaska Airlines and noticed that the carrier even calls this out during the ‘manage your flight’ flow.

It’s rather common for airlines to change departure or arrival times by say 20-40 minutes. A family member recently forwarded me their updated itinerary for a JetBlue flight where one leg of their journey had been changed by over an hour.

An hour isn’t as common, but it’s also not unheard of. Thus, if you can be patient – after all, your failsafe will still be cancelling for the flight credit – to see if you can catch some flight-change-bank-error-in-you-favor-lightning-in-a-bottle, you might end up with the cash refund you desire.