Difficulty buying items

In my Lulu game recently, I was unable to buy ardent censer, even though I had enough money. It was greyed out, while things like Redemption and Mikael's were bright (you can buy these color); however, I couldn't buy them as I did not have prerequisite items. I return to the shop a 2nd time, unable still to buy AC, but I sold my prerequisite items, and was finally able to buy AC.