I've provided them official contract of buying appartment I currently live in + contracts of selling previous appartments + bulgarian permanent resistence card + bulgarian driver licence + bulgarian bank account statement.
yesterday they asked me to provide the ownership of my another appartments in Sofia which I use in airb'n'b + my bulgarian firm bank account statement.
so, it's not enough for them to make sure of my place of residence, now they need to check where I get my money from.
ok, sending it.
Good luck. Although it is not clear to me how many more documents are they going to ask for or how they even verify this kind of information.
CEX seems to utilize the standard ID document + bank statement combination, which seem to be automated. I'm not sure if the source of funds part is also automated but it looks to me like a human is looking at these documents manually.