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In my opinion. If he is from one of those restricted countries. He should not use the platform. Even not try to use them with a VPN. Because, If the platform detects he is from one of the restricted countries. They can ban his account by confiscating his funds. The platform also reserves the right to ask for a KYC. What he would do if the Platform ask for a KYC? So, I guess it's better to suggest to him not to use it if he is from a restricted country.
+1
@Perla
this site updated those restrictions, they have time but they were not long ago, last year I think, the issue here is to be aware of your emails or the ToS update, sometimes they do not send direct emails of each update explaining, if not general, eg "the terms and conditions have been updated, bla, bla," always take these notifications seriously, since not review them can cause what the quote mentions.
It is not your case, fortunately, but I mention it because your concern is a classic that is repeated frequently in the basic use of casinos. Sometimes users get surprises like yours even if they had registered in good faith, but they did it another time; so there are surprises when you have time without login and you are not attentive with the updates.
Some casinos offer update emails for this type of restriction, these restrictions are not permanent, just as countries are added, some are no longer restricted. Check the original source always, the forum is a good indication of where to go but casino rules are constantly changing check them later yourself.