Source of Wealth documents (invoice)

Hello. I need to send documents for source of wealth, for a casino. I am not employed, so to prove my income I sent invoices, but the casino rejected them because the invoice only has my signature (and the client's signature is missing). In my experience, my signature is enough and many other people send invoices even without any signature. I found various types of answers on internet, so I can't understand if the casino's request is legitimate and in compliance with the law, or is it their excuse to reject the invoice. What is your opinion?

Thanks

Hi. May I firstly ask in which casino do you experience this issue?

Does it mean that you are self-employed, yes?

If you see that the casino doesn't accept anything from you and you have problems verifying your account, please let us know, and maybe our complaint team will be able to help.

Currently I prefer not to reveal the name of casino, I want to try to resolve without disputes first. Yes I am self-employed, I work as a freelancer, so to demonstrate the source of my funds (source of wealth), the only method is invoices. I wanted to understand if legally, an invoice to be valid must have both signatures (mine and the customer) or my signature is enough. On internet I have read various different opinions. I think it's an excuse used by the casino to not accept invoices, but I would like to hear other people's opinions

Yeah, I understand. Whenever you are ready, just come forward, of course.

I hope you will be able to solve it out soon, but if you need some legal advice, probably the best is to contact a lawyer. Right?