If you’re trying to purchase an item and you see the notification “Item has a pending transaction,” it means another user is currently trying to purchase the same item.
When you see this notification, you can either find another item in the collection to purchase, or you can try to purchase the item by sending your transaction with a more competitive gas fee.
If you try to purchase an item with a pending transaction, there’s a chance that the other user’s transaction is accepted first, which means you’ll lose a portion of your gas fee and you won’t get the item.
To see the details of the best competing transaction, you can hover over the shopping cart icon in the checkout flow.
In your wallet, you can navigate to the Advanced options and edit the gas parameters for the transaction. For more information about advanced gas controls, you can check out this MetaMask help guide.
These screenshots are from MetaMask, but other wallets should have a similar option.