Hi,
Payment methods will be filtered at display. If you set a zone restriction in the payment settings, the payment method will only be displayed if the address of the user is within that zone. Moreover, the payment methods are automatically filtered based on the current currency. For example, paypal only supports a limited number of currencies and if the current currency is not supported by paypal, the paypal method won't be displayed. Here is a list of the supported currencies for paypal :
cms.paypal.com/us/cgi-bin/?cmd=_render-c...i_nvp_currency_codes