So i tried that just now and when i click on unlock champ, it says error, ''Your purchase could not be completed at this time.'' i don't know what to do, i really want karthus

I did exactly what was said earlier, but it did not resolve my problem! :/

I'm having the same problem. My ip isnt updating in the store and so I cant buy anything.

I tried clicking on the champion to buy them with ip and it isn't working at all

i have the same problem...my store IP doesn't update since i bought an IP boost yesterday

Same here, anyone found a solution?

Exactly same issue too!

Tried both technique from store (which doesn't allow me to click the unlock button at all) and from champion description unlock button (which gives the error message "Your purchase could not be completed at this time.").

Slight difference is that in the store, the amount of IP seems to be like a few days old. I've played 3 games since I noticed the issue and it seems the amount of IP isn't refreshed in the store (or the moment the buy request is done).