This has been a problem for a while, and I've reported a couple of times. Gree is working on it with Apple. Many people have also said they have the same problem. So when a guild-mate, Lorglath, told me a work around that ACTUALLY works, I thought I'd share.

You need to transfer your game to another device that has not had KA on it. I did this on Friday, but first went to a device that had an old game on it. Gems purchased downloaded, but I wasn't able to buy more.

After much tinkering, I was able to get my second device to a KA virgin state, did the tutorial, then the transfer...and then no problems downloading gems...

Make sure that you first go through the tutorial. Then do the transfer. You should be able to get your gems this way.

AK