I have an ASP.NET application that I would like to connect to my Quickbooks Online account to programmatically enter new invoices, make payments against those invoices and even enter new expenses. It seems that there are all sorts of APIs and processes for this that have undergone many changes over the years so I am confused as to where to start. I'm not looking to create a app that I'd release to some sort of App Store or anything, this is just for personal use (automation, etc.) I'm looking for a simple, straight forward, approach.