As it stands the only way to add funds into Digital Ocean is to use Paypal, but the thing is that paypal is not available in some countries.
In addition to that the model of charging the credit card at the end of the month can also fail if the user has disabled his card from being used for online transaction without him informing his bank prior to the transaction.
So i suggest that please allow credits cards to add funds to your Digital Ocean Account.
Currently as it stands i have to activate online transactions every month on my card to pay for the server charges, there is a chance that i may miss a payment, incase i am busy or incase i just forget about calling my bank.
But if your allow users to add funds from credit cards, say 50-100 $ rather than paying on a per month basis, it would be beneficial both for the user and the Digital Ocean. As it will take away the frustration of having to activate online transaction at the start of every month .