In order to deposit or withdraw skins from/to Steam, you must download the Steam mobile app, enable Steam guard on it, and wait 15 days before being able to trade instantly on Steam and gamble here. This is a security measure from Steam.
Canceling Trades, Changing Passwords, Re-enabling it, Disabling it for even 1 second, Changing Phones/Numbers. Doing any of these things will reset your Steam Auth.