Congratulations! If your order is being processed it means someone purchased your item.
During this period, Gameflip verifies the authenticity of the buyer's payment. The order is released after the process is complete. The buyer has no access to the item (e.g. automatic delivery keys or skins) while an order is being processed.
In most cases, the processing period lasts no more than 5 minutes, but depending on the purchase circumstances (e.g. very high-value items), it could take up to a few hours.
Note that if an order is canceled during the processing period, your listing will be put back on sale automatically.