There’s a loophole American uses to get out of honoring 24 hour ticket cancellations/refunds in certain cases.
If you use credit from a previous cancelled ticket to pay for your reservation American tells me that they will not honor 24 hour cancel/refunds. They claim that when you pay for a new reservation using the residual from a cancelled ticket (whether partial or full payment) then it “isn’t a new reservation” so DOT rules under 14 CFR 374 don’t apply. Even for cancellations made less than 15 minutes after purchase, and for reservations that were newly created.