Some of the countries that are restricted from using PayPal and, therefore, cannot make online casino transactions are Afghanistan, North Korea, Central African Republic, Pakistan, Montenegro, Iran, Iraq, South Sudan, Monaco, Zimbabwe, Ghana etc. You can see a full list of accepted markets and currencies here.
IMPORTANT! Bear in mind that Americans can own and use a PayPal account, but not for making deposits and withdrawals at online casinos. Instead, they need to seek out other payment alternatives like VISA, MasterCard, or American Express.