Verification of KYC (Know your customer) is a standard regulation in place for online casino to verify your identity and that you are the owner of the said account in use for deposits and withdrawals. Verification are usually done upon withdrawing from a casino for the first time, however some casino only perform verification after a certain withdrawal amount is requested. When a player wins huge amounts like over 10 000 euros, additional security and verification could be performed. You could also face SOF (Source of funds) or SOW ( Source of Wealth) request, where you need to provide the casino with proof of income or heritage or any source of possession which is highly valuable to show that you have the funds necessary to gamble.