The items you purchase in Design Home cost Diamonds or Cash. You can use your Cash to buy Inventory Items with the $ (Dollar Sign) underneath that Item, and alternatively, you can use your Diamonds to buy Inventory Items with the Diamond Symbol underneath.

If you run low on Diamonds, unfortunately, you will not be able to use your Cash to make up for the cost of an Item that costs Diamonds.

However, if you are running low on Cash, you can use your Diamonds to purchase more Cash.