Temple of Time Ornate box Question

So I went to check whether anything good was in the box and this came up.

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When I tried to buy the item this message comes up.

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So my question is why does this pop up?

There's only a limited stock of that item in that shop. Once it gets bought up by players, it's unavailable until it is restocked in the shop.

There's only a limited stock of that item in that shop. Once it gets bought up by players, it's unavailable until it is restocked in the shop.

One time I get lucky, but the luck still isn't enough. Thanks for answering.