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Have you ever read the terms of Blackjack.fun? They reserves the right to request for KYC verification
9.3. We reserve the right to request photo ID, address confirmation or perform additional verification procedures (request your selfie, arrange a verification call etc.) for the purpose of identity verification prior to granting any withdrawals from your Account. We also reserve our rights to perform identity verification at any time during the lifetime of your relationship with us.
Blackjack.fun hasn't applied this rules on you as you haven't done anything wrong there. But they may ask you to do that if they find anything suspicious. They may request to get all kind of personal documents from you. I have mentioned about those in the table. They have dedicated page with the information of KYC verification system:
https://blackjack.fun/kyc-policyI'm regularly playing at many casino since last few years. Most of them reserves the right to request identity documents. I have made withdrawals few hundred times, but none of them ever asked me to go through the KYC process except two casino.