Casino sends money to US NETELLER account ,money is stuck there .The act of then taking it from the usa Neteller account and sending it to a casino is illegal As it would count as transfer from US citizen.
Had the casino cancelled it before you click ‘accept’ then that is allowed.Just a legal technicality that will probably come up.Now if the casino bounced a payment i am sure they would find a way to take the money back from you and not consider it breaking the law 