So I am thinking that the purchase will happen in-game ? therefore we need some sort of overlay with an iframe to allow for the invoice to be shown. One could use BIPS embedded Invoice each time a player wants to purchase "gold"
https://bips.me/embedded simply generate this invoice with a custom variable containing the players "user id".
However this would require a system able to receive Instant Payment Notifications from BIPS as to update the in-game currency.
Another way would be to create a C# framework, I have chosen C# as this is one of my main languages. This C# framework could be created as an dll to be included with say BIPS as namespace, and included in games. This would give the possibility of simple running:
BIPS.CreateInvoice(100, 'USD', 'Gold', 'userid', function(err, res) {
/**
Example response (Bitcoin address, and amount)
*/
ShowInvoice(res.address, res.amount);
});
private function ShowInvoice(string[] address, double amount)
{
/**
Display a nice payment window to the user using DirectX Hardware Overlay.
*/
}