I think I like the service you are offering at xmint.org
But I couldn't send, so I cannot answer your question: "What is your invoice id"
I cannot get the id, without sending coins, and all I have is a smartcoin wallet and bitcoin wallet.
So, you would need to accept smartcoins, and then I could send smartcoins, and have the smartcoins exchanged into bitcoins.
I would really like that.
That would make my day, if you would accept smartcoins for exchanging at xmint.org
you need to use the early access URL sent in the PM to access the site.