Audio player not working

First thing I'd do is check the fuses, although these are probably fine if the radio turns on - but a lot of these cars use the 12V fuse to power both, so check the fuses for the cigarette lighter and check it with a DMM first - if you pull the 12V cigarette fuse and radio fuse for 10-15 minutes to reset it, this could help as well if the fuses are not blown. A lot of these old cars before DCTs normalized NVRAM TCMs use volatile KAM for ECU and TCM data, and it will ride jerky until it relearns.

If it doesn't help or they are good, try another aux cord - doesn't need to be premium, a cheap cable will suffice as they're all the same thing. Depending on the age of your old cable, these aux cords have short lives compared to a USB-C cable over CarPlay/Android Auto. It's likely your cable. As a last resort you can try CRC QD contact cleaner and see, but if that does not help the jack is 100% dead.

If it doesn't help, the jack is bad in the sense the sense pins are worn. Kia puts it in the center console/shifter area, so you need to partially tear the car down to replace it as you can't just replace the radio. This site has the SM for your car: https://www.allcarmanuals.com/factory-se... -- I found the P/N for this car, but it's just not well documented like the newer cars are :-( -- anyway, now it is: 96120-1G200-X5 OR 96120-1G200W6 -- X5 is the hatchback, W6 others. That said, you can probably find it in a junk yard given how many of these get totaled mechanically due to minor issues or oil consumption. That said if it were mine, I'd just put a modern CarPlay/Android Auto radio in that can do USB CarPlay/Android Auto and modernize it vs find old Hyundai parts.