probably best bet is to send a private message to a moderator and ask them.
That won't help because the mods are receiving hundreds of messages everyday so do you think you'll get noticed?
my friend's account is not allowed to post or send private messages in this forum.
Your friend has been banned.
I also do not know what violation is done, maybe because of the post that is not recommended, and told to appeal.
You can know the reason of that ban if you're going to post it on the
Meta.
but I do not know how to appeal.
You can post your appeal there but I doubt that you can recover your friend's account because it was banned for a reason, either for copy pasting or doing something against the forum law.
which I found out how to redeem by sending some bitcoins to a specific address.
What's with this?