The live price shows all pending buy and pending sell requests made by other users on the Live Exchange. These are requests that did not have any direct matches available at their preferred price.

When there are no pending requests in the Live Exchange for the item selected, the button will be disabled.

To add your preferred price to the live exchange, you can refer to the tutorial here: https://help.ibxhk.com/en/articles/8693681-how-do-i-sell-gold-or-silver-using-the-preferred-price-option-on-the-ibx-exchange