It would be better if you have proof of how you are receiving your salary from your workplace. Or I think a bank statement of account should also be enough as an evidence. I think the transactions on electrum is not enough. Or are you paid in bitcoin in your country? If so, the gambling site customer care will ask you questions about it and they will still need proof from the company you are working from.
This, when casinos ask for an income statement, what they want is for the gambler to verify with them how they get money, however even if a person is earning bitcoin somehow this is not going to be enough as this is part of their KYC verification process, so the OP needs to show a document from their company or bank that allows the bank to verify their identity and the amount of money they earn, and if the OP cannot do this then it is unlikely they will pass this verification.