If your documents are notarized and apostille and if the OKPAY's company jurisdiction is part of the Hague Convention, then OKPAY MUST accept your documents.
If OKPAY jurisdiction is not part of Hague Convention then your docs must be legalized by the diplomatic/consular mission of OKpay's jurisdiction(i don't know who it is) in your country.
So, find out where OKPAY is registered
I did as I was asked by them initially and sent the documents were I was requested.
Finding out where okpay is registered proves to be somewhat complicated because they like to keep their jurisdiction section blank on their site.
Never mind, I will keep you updated on the actions taken against them.
Either okpay or their financial service provider must clarify it.