I had the same problem with the key for my Hundy, well, kind of.
My ignition key is a different cut than my doors. Bought it that way. I guess the previous owner had to replace the ignition key at one point. My valet key will twist in the door lock, but not in the ignition.
Anyways... The buttons on the 3 button master key didn't work when I first bought this rig either. So I had to have 2 sets of keys, my valet key to get me in and the 3 button master to drive all the time.
Sooo... I bought a new battery for the key, still didn't work. Then I had to take the key apart, and I re-soldered the four posts for all the buttons.
Amazingly!! All the buttons worked! They way I could tell is after I soldered a button, I placed the battery back in and pressed the new soldered button and if the little red LED lit, I knew it would work on the car.
Now I have a perfectly working 3 button master key. Albeit, just one, hence my thread elsewhere on getting other keys.
Tip if you try soldering, get a very small soldering tip.
First I unscrewed the case.
Popped out the chip and used a razor knife to carefully split open the chip case. Work the razor knife around the perimeter of the case to split the glue seal. It's not too hard if you're careful.
There's nothing too delicate in there, (I'm referring here to there's no little wires or circuits to bend or break off) and nothing to drop out, so don't worry about that. Just don't jam the knife to far in when splitting it. The soldering can be a depending on your soldering skill and how steady your hand is.
When you think you soldered it, with it all apart, drop the battery in and press the little button and see if the little red LED comes on. If it does, wa-laa! You did it and it works!
As a side note, depending upon our age, if you're like me I used a magnifying light, or you can use a magnifying glass or high power reading glasses to work with. It will be small, that's why the double bananas for difficulty.
back to OP: seems like you answered the question yourself. If by manually you mean "turning it" then I would think that if it does not work in any of the doors and the other keys do work fine then it's just the key metal being worn (if it worked before) or poorly cut.