I'll paste here what I pasted another dev, who sadly seems mia likely due to personal and professional reasons so please contact me and let me know what questions you have more about it if interested
Willing to pay fair and more for swift work.
So, what I need is the following. You need not worry about the portion where I consume and make use of these APIS, just that the apis exist. If you still need a flowchart for this, can you be a bit more specific on what you wish it to contain
**addpaidinvoice**
/// Purpose: To add an invoice marked "paid" to a user.
/// Parameters:
/// @ Product ID to add as a paid invoice for the user.
/// @ Users OAUTH token (note: if this is too hard, i can accept user id and handle the oauth verification on my end np) (I set up a custom OAuth for the external site already)
/// Other Requirements: Must be able to be restricted to an IP address so that only my servers IP can consume the API
/// returns: 200 https or failure code
One more note, the addpaidinvoiceapi should accept discount codes as well, and unless the discount makes price $0 then it should display a succes code otherwise an error code and or message.