Jeffrey there isn't a specific video that deals with exactly that. Richard Tech Help Database it is a good start.
Looking at the courses you have taken so far, I think you might need external help to get this thing done. Check the following: https://599cd.com/blog/display-article.asp?ID=1584

The only one I can think of doesn't specifically deal with customer and vendor, but it does show changing a quote to an invoice and then to a paid receipt. Quote, Invoice, Receipt

Another video that you might get some ideas from is the Help Desk video. The customer makes a request (ticket) then you can track the status of the ticket through as you get info from vendors then eventually turn it to the invoice status and, if you were a gold member, it shows how to automate the process all through billing.