Do you mean something like Bitpay?
https://bitpay.com/api (?)
BitPay provides a standards-based REST interface which enables application developers to interact in a powerful, yet secure way with their BitPay account. Using the BitPay API, clients can create and manage invoices, issue refunds, manage bills, retrieve real-time rates information, view merchant ledger entries, and much more. Developers may call the API directly over HTTPS using the language of their choice, or take advantage of one of BitPay's Node.js, PHP, and Ruby API clients.
I'm not entirely sure what their fees are, and if you
really want to use them, since i'm pretty sure you'll be forced to use BIP70 aswell, which can be quite inconvenient for some customers..