What is the invitation code for CoinW?

Excuse me, I'm trying to sign up for CoinW, but I'm having trouble finding the invitation code. Could you please clarify what exactly the invitation code is for CoinW and how I can obtain it? Is it something that's required for registration, or is it optional? If it's necessary, could you provide me with an example of a valid invitation code or guide me on how to get one? Thank you for your help.