Create "Add Funds" invoice via Admin API
There is no way to fully use the credits feature if you've integrated WHMCS to your own system and don't let customers access the WHMCS client area. It's only possible for the client to see current credits (via GetCredits), but there is no way for the client to create an Add Funds invoice and add credits to the account. This is an important part of the WHMCS system and there should be an API call for it. Not everyone use the client area, and for us who use the API, the whole credit system is useless.