Well, have you read this in TOS? If not check it carefully or ask the OP here or reach out to the Blackjack.fun's support ^{[ info@blackjack.fun ]}.
I have read it and it seems a long paragraph there which I don't know if I skipped about using the VPN part, but it was stated there once you log in using different credentials or if they will find out --your account will be under the compensation status.
Ask them or wait for a reply here, because usually in most gambling casinos VPN does not allow it even though this was not mentioned on TOS and FAQ you should clarify it first.