We recently started selling services internationally, however the fees associated with Credit Cards and PayPal are so high that for now, we've decided to only accept bank transfer for International customers. Unfortunately, there's no way to force this. While asking a customer to pay using this method, they chose to pay via PayPal (a valid option here in Australia). The result (after exchange rate and fees) was a net $300 loss on the transaction.
It would be nice to limit the payment methods available to some clients, either by creating "payment method groups" or something similar, so that in future, we can customise the features and processes available to specific customer groups.
Future enhancement of this idea could then allow each customer group to have different rules for reminders, automation etc. which would make the system much more flexible when managing multiple brands, products or services within the one system.
I make referencing to this similar feature request, which although we would find useful, is perhaps a little less flexible (but is now closed for comment): https://requests.whmcs.com/topic/force-one-payment-type-lock-for-certain-customers